Add a new file and a few functions for dependency management.
Fix a few typos and forgotten imports.
Use the new dependencies module for installing deps.
Move the find_required function to dependencies
Drop find_required from build.py.
Use the new dependencies stuff in test.py
Bump snake version.
Move a few imports around, and add some docstrings.
Merge pull request #77 from NarrativeScience/feature/refactor-deps

Refactor deps