add libpng support
remove libpng from todo.txt
cpuimage: replace is_rgba with a generic pixel format field
glimage: always unbind the texture image after drawing
glimage: don't draw sections of the slices that don't exist
glimage: read non-RGBA/BGRA slice data properly

code was assuming channels=4 in all cases, which is no longer true
image-libpng: use RGB color space if available
image-libjpeg: use minimal pixel format, add support for YCC(K) images
image-libpng: remove blank line
cmake: include debug symbols (-g)
todo: on cmake now, is sane
glimage: import grayscale images with GL_LUMINANCE, not GL_RED
image-libpng: support gray pngs
cpuimage: support CPUIMAGE_GRAYA as a pixel format
flags.txt: add ENABLE_LIBPNG
image-*: don't bother clearing unused bytes to 0 anymore
image-libpng: plug major memory leak
inklog: logging framework added
inklog: disable timestamps by default
filetype: refactor into two functions and constants for the type