Use external colorlib

This is a work in progress branch.

Goals of this refactoring:
- [x] Get rid of all the internal color libraries
- [x] Keep the CSS as untouched as possible, keep it useful
- [x] Keep the line and column numbers for useful feedback
- [ ] Make the rendering of each color in the command line output recognizeable by showing both the matched color and the hex color (optional)
- [ ] Improve the rendering of each color with filename, line number, column number (optional)
- [ ] Make sure nothing is broken
synesthesia, which generates the regexes for the colors, is pulling in css-color-names in the same version. So that has it.
I had to add rebeccapurple to one-color yesterday in order to make the css-colorguard test cases run :)