Merge pull request #3 from Nuke928/master

Add basic unit tests
Rename id to id_number in README.md since id is reserved
Migrate unit tests from unittest to py.test for easier and more flexible testing
Update API documentation link in __init__.py
Fix random sorting parameter breakage for sf=
Undo change to sort.RANDOM since parameter has been fixed
Add test_random_parameters.py to verify correctness of derpibooru.sort
Remove extra source_url string in query.py
Add mp4 and webm file representations for gifs
Do not use the 'search' index