Merge pull request #49 from iger/master

Some changes in comments
Fixing some comment inconsistency regarding PixelYCbCr (fix #50)
Fixing problems with criterion.
Fixing loading of progressive jpeg images with more than two huffman table (fix #51)
PixelYCbCr8 - a missing correction in comment
Standardize (now fixed) description of PixelYCbCr8
These should be separate sentences.
Clean up description of unsafeExtractComponent
Use proper deprecation pragma.

It would be nice to state in which version the function will be removed.
Cross reference comments on floating point pixels.
align columns
Expand and stylize description of Image type.
Expand description of DynamicImage