Library should use ':type'/':rtype' or pep484 compliant typehints

By adding the ':type' and ':rtype' it improves autocompletion / static analysis in IDEs. Alternatively PEP484 (typehints) was updated recently to add Python2.7 (and technically prior) compatibility: https://www.python.org/dev/peps/pep-0484/#suggested-syntax-for-python-2-7-and-straddling-code