Added out-of-bounds handling for hslToRgb function with unit tests

I've added out-of-bounds handling for the `hslToRgb` function. It normalizes the hue orientation between 0 and 360 degrees and ensures that saturation and lightness are between 0 and 100. I based tests of this functionality on the Webkit CSS tests here:

<http://trac.webkit.org/export/98524/trunk/LayoutTests/fast/css/hsl-color.html>