Support parametric color types
Switch to Ufixed8 for 8-bit images
FixedPoint->FixedPointNumbers
Remove RGB8 and fix some scaling issues
Have the NetPBM reader return Ufixed or RGB{Ufixed} types
Remove limits, move everything to ColorValues (monolithic change)
Change OSXnative reader to use ColorValues
Significantly expand testing of core
Split uint32color into separate file and make several improvements

- More no-op conversions to Uint32
- Generalize red, green, and blue functions
Add deprecations for some functions used by ImageView.
Improve `convert` and add `reinterpret` and `separate`
Fix writemime scaling problem
Start documentation changes
Introduce ColorType Union and length(::ColorType)
Support float32(::Image{RGB{Ufixed8}}) and similar
Fixes/improvements to conversions
Fix setindex!
Fix concrete type in colorspace conversions
Get imfilter working for ColorValue arrays
Fix saturation example, view(2*img)