Add Python builtin function highlighting

[ecterceocgan]

List of builtin functions comes from: https://docs.python.org/2.7/library/functions.html

[Golmote]

Hi @erinwild! Thanks for contributing.
Would you mind adding/updating the tests for this (see http://prismjs.com/test-suite.html and existing tests: https://github.com/PrismJS/prism/tree/gh-pages/tests/languages/python).
Also, please run gulp on your local version to generate the minified version of the component.

[Golmote]

While you're at it, could you also add the nonlocal keyword, requested in #1208 ?

[ecterceocgan]

@Golmote Done!