Add hwb() + fix max for hue

Following

harthur/color-string#8
harthur/color-convert#10

+

capping must be done before convert loop for each spaces.
Otherwise it’s not coherent with how color-convert handle overflow
(modulo).

Ref #24
Before doing that, I just want to be sure that you understand [my previous comment](https://github.com/harthur/color/pull/25/files#r14982533).
If I do that I'll have to add a weird test 

```
assert.equal(Color({h: 400, s: 50, l: 10}).hue(), 360); // existing test
// ... later
assert.equal(Color({h: 400, w: 50, b: 10}).hue(), 0); // 0 ? Yes. Because `hue()` use hsl: hwb channel have been correctly set to 360, but conversion changes hsl hue to 0.
```
Note: conversion responsible for the 360 -> 0 https://github.com/harthur/color/blob/72efbc775e97e649c00403d425888fd9d4e27bfa/color.js#L343

Are you sure you want that ?