Fix a DIN99d bug
Add colortype
Merge branch 'master' into teh/colortype

Conflicts:
	src/colorspaces.jl
Merge pull request #62 from JuliaLang/teh/colortype

Add colortype to simplify working with the type hierarchy
- Undefines errorneous +, * on LCHUv
- Defines +, * on XYZ as a linear vector space
- Defines +, * on all other ColorValues using intermediate arithmetic in
  XYZ space
Add tests for vector space operations in color space