Adds closest_match functions for color matching among RGB colors. to_lab helper function also added. UnitTests created, all green.
Cleans up code slightly. Converts hash to 1.8.7 hashrocket syntax. Improves documentation. Reverts gemspec modifications and deletes empty lib/color_match.rb file
Add Color::RGB#closest_match using…

…the CIE Delta E 94 algorithm.

- Based on work by Aaron Hill (@armahillo), adapted to the Color
  codebase conventions by Austin Ziegler (@halostatue).

- Fixes #5, reported by @armahillo.