support PGM and PPM formats
treat vertical tab and form feed characters as whitespace
Merge branch 'master' of https://github.com/kennethdmiller3/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/kennethdmiller3/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'working' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/nothings/stb
Merge branch 'master' of https://github.com/kennethdmiller3/stb
Merge branch 'master' of https://github.com/nothings/stb
VC6:
  support using inline asm for cpuid

YCbCr:
  switch SSE code to constants that match old C;
  create C version that is same as SSE;
  tiny optimization(?) of SSE
finalize scalar YCbCr conversion back-ported from SSE version;
add missing STBIDEFs to a few functions;
update documentation with full 1.49 info even though most isn't implemented yet
STBI_MALLOC etc.
some documentation cleanup
Merge branch 'master' of https://github.com/kennethdmiller3/stb into ppm
PNM cleanup
fix a few old error messages
tweak release docs
tweak credits
tweak revision history
remove trailing whitespace
stb_image: JPEG resampler func for NEON