Mep21 improved color and cm modules

This MEP has not commenced yet, but here are some ongoing ideas which may become a part of this MEP:

• color
  • tidy up the namespace
  • Define a "Color" class
  • make it easy to convert from one color type to another hex -> RGB, RGB -> hex, HSV -> RGB etc.
  • improve the construction of a colormap - the dictionary approach is archaic and overly complex (though incredibly powerful)
  • make it possible to interpolate between two or more color types in different modes, especially useful for construction of colormaps in HSV space for instance
• cm
  • rename the module to something more descriptive - mappables?

Overall, there are a lot of improvements that can be made with matplotlib color handling - managing backwards compatibility will be difficult as there are some badly named variables/modules which really shouldn't exist - but a clear path and message for migration should be available, with a large amount of focus on this in the API changes documentation.