v0.12.0

Implemented more hue fixup methods (#93):

• add fixupHueShorter(), fixupHueLonger(), fixupHueIncreasing(), fixupHueDecreasing() methods;
• alias interpolateHue() to fixupHue() — the former will probably be removed from the API at some point
• add fixupAlpha() method, slightly different than the old interpolateAlpha();
• alias interpolateAlpha() to fixupAlpha() — the former will probably be removed from the API at some point

New methods:

• formatHex8()
• mapper()
• mapAlphaMultiply()
• mapAlphaDivide()
• interpolateWith(premap, postmap)
• interpolateWithPremultipliedAlpha()