Color 1.7.1, rename BeccaPurple to RebeccaPurple
Start color 2.0 work.

- Remove explicit support for Ruby 1.8 from Travis.
- Remove deprecated methods and constant warnings.
Standardized on `alias_method` instead of `alias`.
Reduced iterations on assignment.
Added methods to Color::RGB to calculate the contrast between two RGB colors
Added additional contrast method which implements e2000 method for computing contrast. Added tests for this and existing #contrast
Added e2000 contrast method and hand-made contrast method
Putting lab stuff into its own area, and correcting references to lab objects to reflect
Left #closest_match same as it was, but fully qualified #delta_e94 reference
Fix a bad merge conflict resolution.
merged CIE-Lab-class branch