Preliminary optimisation
Second optimisation pass
Optim pass 3
tmp
This commit mark a step in optimisation,
Juicy.Pixels is now at 4x the performance of imagemagick for
compression/decompression of JPG/PNG
Handling quality of 0 for jpeg decoding, should handle #17
Optim pass + new comments
Use mmapFileByteString instead of withFile/Data.ByteString.hGetContents

It's about 64 times faster for reading (without decoding!) the ~3MB huge.png file, and 150 times faster for reading (without decoding, again) the ~6MB huge.jpg file. mmapFileByteStringLazy sits in between the strict version and the hGetContents version, significantly faster that withFile/B.hGetContents.
Optimising block unpacking
Avoid copying PNG data during encoding, directly blit Vector into bytestring
Faster YCbCr -> RGB conversion
Avoiding some useless zeroing
Fixing regression when image height is not a multiple of 8
Fixing some testing display
Bliting vectors in BitWriting
Fast RGB->YCbCr conversion
Diverse tiny optimisations
Merge remote-tracking branch 'mestan/master'
Script to swtich array access to safe ones
Adding Eq instances for pixels