Crush all the pngs.

Output Log:
** Processing: Textures/default.png
16x16 pixels, 4x8 bits/pixel, RGB+alpha
Reducing image to 8 bits/pixel, 29 colors (27 transparent) in palette
Input IDAT size = 206 bytes
Input file size = 263 bytes

Trying:
  zc = 9  zm = 9  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 7  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 6  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 5  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 4  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 3  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 2  zs = 0  f = 0		IDAT size = 119
  zc = 9  zm = 1  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 9  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 8  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 7  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 6  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 5  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 4  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 3  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 2  zs = 0  f = 0		IDAT size = 119
  zc = 8  zm = 1  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 9  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 8  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 7  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 6  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 5  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 4  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 3  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 2  zs = 0  f = 0		IDAT size = 119
  zc = 7  zm = 1  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 9  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 8  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 7  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 6  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 5  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 4  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 3  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 2  zs = 0  f = 0		IDAT size = 119
  zc = 6  zm = 1  zs = 0  f = 0		IDAT size = 119
  zc = 5  zm = 9  zs = 0  f = 0		IDAT size = 118
  zc = 5  zm = 8  zs = 0  f = 0		IDAT size = 118
  zc = 5  zm = 7  zs = 0  f = 0		IDAT size = 118
  zc = 5  zm = 6  zs = 0  f = 0		IDAT size = 117
  zc = 5  zm = 4  zs = 0  f = 0		IDAT size = 117
  zc = 5  zm = 3  zs = 0  f = 0		IDAT size = 117
  zc = 5  zm = 2  zs = 0  f = 0		IDAT size = 117
  zc = 5  zm = 1  zs = 0  f = 0		IDAT size = 117
  zc = 5  zm = 6  zs = 1  f = 0		IDAT size = 117
  zc = 5  zm = 4  zs = 1  f = 0		IDAT size = 117
  zc = 5  zm = 3  zs = 1  f = 0		IDAT size = 117
  zc = 5  zm = 2  zs = 1  f = 0		IDAT size = 117
  zc = 4  zm = 6  zs = 1  f = 0		IDAT size = 117
  zc = 4  zm = 4  zs = 1  f = 0		IDAT size = 117
  zc = 4  zm = 3  zs = 1  f = 0		IDAT size = 117
  zc = 4  zm = 2  zs = 1  f = 0		IDAT size = 117
  zc = 1  zm = 9  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 8  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 7  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 6  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 5  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 4  zs = 2  f = 0		IDAT size = 109
  zc = 1  zm = 3  zs = 2  f = 0		IDAT size = 109
  zc = 9  zm = 9  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 8  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 7  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 6  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 5  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 4  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 3  zs = 3  f = 0		IDAT size = 107
  zc = 9  zm = 2  zs = 3  f = 0		IDAT size = 107
                               
Textures/default.png is already optimized.

** Processing: Textures/plane.png
16x16 pixels, 4x8 bits/pixel, RGB+alpha
Reducing image to 2x8 bits/pixel, grayscale+alpha
Stripping metadata...
Input IDAT size = 339 bytes
Input file size = 470 bytes

Trying:
  zc = 9  zm = 9  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 7  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 6  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 5  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 4  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 3  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 2  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 9  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 8  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 7  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 6  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 5  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 4  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 3  zs = 0  f = 0		IDAT size = 247
  zc = 8  zm = 2  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 9  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 8  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 7  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 6  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 5  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 4  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 3  zs = 0  f = 0		IDAT size = 247
  zc = 7  zm = 2  zs = 0  f = 0		IDAT size = 247
  zc = 9  zm = 9  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 8  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 7  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 6  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 5  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 4  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 3  zs = 1  f = 0		IDAT size = 234
  zc = 9  zm = 2  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 9  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 8  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 7  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 6  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 5  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 4  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 3  zs = 1  f = 0		IDAT size = 234
  zc = 8  zm = 2  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 9  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 8  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 7  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 6  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 5  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 4  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 3  zs = 1  f = 0		IDAT size = 234
  zc = 7  zm = 2  zs = 1  f = 0		IDAT size = 234
  zc = 5  zm = 9  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 8  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 7  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 6  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 5  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 4  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 3  zs = 1  f = 0		IDAT size = 232
  zc = 5  zm = 2  zs = 1  f = 0		IDAT size = 232
                               
Selecting parameters:
  zc = 5  zm = 2  zs = 1  f = 0		IDAT size = 232

Output IDAT size = 232 bytes (107 bytes decrease)
Output file size = 289 bytes (181 bytes = 38.51% decrease)

** Processing: Textures/rover.png
16x16 pixels, 4x8 bits/pixel, RGB+alpha
Reducing image to 2x8 bits/pixel, grayscale+alpha
Stripping metadata...
Input IDAT size = 424 bytes
Input file size = 555 bytes

Trying:
  zc = 9  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 3  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 8  zm = 3  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 7  zm = 3  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 6  zm = 3  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 5  zm = 3  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 9  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 8  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 7  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 6  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 5  zs = 0  f = 0		IDAT size = 333
  zc = 4  zm = 4  zs = 0  f = 0		IDAT size = 333
  zc = 9  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 8  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 7  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 6  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 5  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 4  zs = 1  f = 0		IDAT size = 321
  zc = 9  zm = 3  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 8  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 7  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 6  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 5  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 4  zs = 1  f = 0		IDAT size = 321
  zc = 8  zm = 3  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 8  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 7  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 6  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 5  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 4  zs = 1  f = 0		IDAT size = 321
  zc = 7  zm = 3  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 8  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 7  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 6  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 5  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 4  zs = 1  f = 0		IDAT size = 321
  zc = 6  zm = 3  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 8  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 7  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 6  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 5  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 4  zs = 1  f = 0		IDAT size = 321
  zc = 5  zm = 3  zs = 1  f = 0		IDAT size = 321
  zc = 4  zm = 9  zs = 1  f = 0		IDAT size = 321
  zc = 4  zm = 8  zs = 1  f = 0		IDAT size = 320
                               
Selecting parameters:
  zc = 4  zm = 8  zs = 1  f = 0		IDAT size = 320

Output IDAT size = 320 bytes (104 bytes decrease)
Output file size = 377 bytes (178 bytes = 32.07% decrease)

         263         257  97% Textures/default.png
         289         289 100% Textures/plane.png (Unsupported bit depth/color type, 8/4)
         377         377 100% Textures/rover.png (Unsupported bit depth/color type, 8/4)
         929         923  99%
Merge pull request #2 from dak180/topic/pngcrush

Crush all the pngs.