Bumps database port back to mongodb default.
Declares database name as a constant in settings.
Renames collections and rewrites module doc string.
Explodes build_mongo_query function into two separate functions.
Explodes query_mongo function into two separate functions.
Rewrites function doc strings.
Uncomments passing tests.
Adds test indices to data_structure file.
Fixes data types in test test_a_known_search_of_two_words_returns_expected_indices to pass tests.