Posterize option
Restored include for USE_SSE macro
C89
Deleted unused struct
USE_SSE opt-in
Simplified optimization flags
SunOS compatibility

Fixes #49
Add include directories conditionally to avoid warnings
PIC in DLL
Fixed calling of sub-makefiles with flags
Markdown formatting
Manual updates
Discourage use of libpng 1.2
convert pointer to integer before performing arithmetic

fixes mempool issues on platforms where sizeof(struct mempool) & ALIGN_MASK != 0
Tell libpng to expand all types to support RGB+tRNS images
Version bump
Removed unused function
Ability to write PNG file only up to predefined size
--skip-if-larger option
Add -msse2

Fixes #65