Add "normalize" function for Unicode about purescript-strings

[MonoidMusician]

FWIW there is another package now: https://pursuit.purescript.org/packages/purescript-unorm/0.0.0/docs/Data.String.Normalize#v:nfkd

[chexxor]

Looks like that one is a binding to a Node lib [1], which is polyfill.
According to MDN [2], most browsers support normalize, so we shouldn't need a polyfill. I wonder if ES 2015 is an important consideration, though.

[1] https://github.com/walling/unorm
[2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize, most browser

[hdgarrood]

I'm keen on adding this, especially given that all modern browsers support it. The only potential issue is what we do on platforms which don't support it. I think we have two options:

1. Just return the same string, and call console.error explaining that normalize wasn't available and that this might break things,
2. Throw an error immediately.

I'm not sure which of these I prefer, but I'm leaning towards the latter.