Refactor me.Color

- `setColor` now properly validates the color components given
- All manipulations go through the `setColor` setter, allowing component validation at the edge
- Marked the r, g, b, and alpha properties readonly, to avoid users trying to change them without using the setter
- Changed `add` blending function to average the alpha components
- Added a `lighten` function
- Added a new parser for RGB[A] format
- Color parsers now cascade, meaning parseCSS can handle all color formats (except HSL[A] -- But nobody uses it anyway. :)
- Added reminder comments to memoize (cache) the results on some functions. The caching should be done cautiously, since there are 2^24 possible color inputs, and some ridicouls number higher if you account for the alpha component.
- Made documentation slightly prettier in some places
- Normalized all method argument names
- Reordered functions, grouping them by operation
- Replaced tabs with spaces, and stripped trailing whitespace