Added typing information and fixed bug in `sentence`, `paragraph`, and `text` functions

[Ahsoka]

This pull request will make this code only compatible with Python 3.5 and higher. If you want to preserve backwards compatibility with older versions of Python, only include the first two commits of this pull request, https://github.com/sfischer13/python-lorem/commit/7175063ef9a5f8399ff3a9867ea05cbde2dc90c3 and https://github.com/sfischer13/python-lorem/pull/2/commits/592a9559a42ecb3b6e02db3e1a2a735a96ef78b5, in versions that you wish to preserve backwards compatibility.