Custom formatting

These commits implement the suggestion in issue jquery/globalize#88.
The format is heavily based on [C# number formatting](http://msdn.microsoft.com/en-us/library/0c899ak8\(v=vs.110\).aspx) (pretty similar to most other languages).
It doesn't currently support: number scaling, percent, per mille, exponential notation.

Compared to the [previous PR](https://github.com/jquery/globalize/pull/112), merge commits and unrelated code were removed.