Fix grammar (s for plural)
Fix description for colorMap

Function colorMap applies a function to all components.
Applying to colors would imply it doesn't apply the function
to the alpha plane of RGBA images, as it is questionable
whether transparency could be called a color.
It also has dubious meaning for Y, YCbCr etc.

It should probably be called componentMap, planeMap or something.
Standardize pixel type descriptions.

Descriptions should now state more clearly that the number of bits
describes bits per channel, not total number of bits.

Descriptions are made to have the same format for easier comparison,
clearly stating each component by name, except for YCbCr,
which needs more care.
missing whitespace
Remove space before a colon. Customarily a colon is directly behind a word.
fix typo
Merge pull request #49 from iger/master

Some changes in comments