Implemented a Typescript definition

[DenisCarriere]

Please review typescript definition @mourner. Added JSDocs to definition @tmcw must be happy :)

Importing polylabel with Typescript looks like this:

import polylabel = require('polylabel')

It would be nice to define the default module to make it the import look like this.

import polylabel from polylabel
// OR
import * as polylabel from polylabel

The JSDocs outputs pretty well using VS Code or Atom.

[mourner]

Thanks!