Switched to Stylus' HSL Implementation

Even though the results produced when adjusting black were the same as stylus, it did not hold true for other colors. This led to `shade` statements adjusting the hue of the colors produced. It also made for bad compatability with `stylus` based `.styl` files (people that switched to rework from stylus).

I have taken the code verbatim from Stylus for this implementation so we should get consistant results across the board.

I also switched the dir structure around in case we need to add stuff to `lib`. Initially I thought I was going to have to write the `rgb2hsl` functions by hand but found them in a library.