Added support for any color format (not tested), opacity and outputs rgba

Never coded in Objective C before, and this is a bunch of copy pasta, so be warned.

Changes:

* Added functions from https://github.com/lifedispenser/ColorPicker/blob/master/NSColorAdditions.m
* Input now interprets many different correct color formats (hex, rgb, rgba, hsl, etc)
* Opacity turned on
* Outputs to rgba() instead of hex.

TODO before merge

* Tests to make sure I didn't leave anything segfaulting
* There can be a smarter output instead of just outputting rgba. If opacity is 1, then output hex. Otherwise, output rgba.