Fix __repr__ of WordList slices on Py3

fixes #52
Fix doctests in quickstart.rst
Add download_corpora module
Delete download scripts and update docs
Use mock for testing translator
Test against pypy on travis
Don't install numpy on travis pypy build
Don't run doctests on pypy build
Take 2
Don't test against pypy (incompatible with nltk)
Bump version -> 0.8.4