Polyad colors

[jpwesterhof]

• Adds functionality to not only get triad and tetrad colors from a color
  but also n-ad colors using n as an argument. n = 3: triad, n = 4:
  tetrad, n = 5 pentad, etc...
• Added more convenience functions like the existing triad and tetrad.

[jpwesterhof]

I was a bit messy with my first two commits, because I copy pasted it from code I currently use. Hence the two follow up commits with fixes to these two forgotten characters (, and ;).

[bgrins]

Alright, sounds good. I'd rather only export triad and tetrad (and not export all the others), but then expose the new one that allows a variable number of outputs. I believe we could call it 'polyad', which is what I could find as the name for these groupings: https://en.wiktionary.org/wiki/polyad

[jpwesterhof]

Done

[jpwesterhof]

Forgot about the internals... done

[thaliaarchi]

This sounds like a cool idea. These need to pass arguments to _applyCombination like the other public methods. So, just make the private triad and tetrad functions call polyad with 3 or 4 as n.

triad: function() {
    return this._applyCombination(triad, arguments);
},
tetrad: function() {
    return this._applyCombination(tetrad, arguments);
},
polyad: function() {
    return this._applyCombination(polyad, arguments);
}

...

function triad(color) {
    return polyad(color, 3);
}

function tetrad(color) {
    return polyad(color, 4);
}

[bgrins]

Landed this in #250. Thanks @jpwesterhof and sorry for dropping this