Sports.py

Fix bug where soccer matches could not be retrieved

Add defusexml as a required package in setup.py

Fix ValueError when parsing matches with no score
Use `defusedxml.ElementTree` to parse XML instead of `xml.etree.ElementTree`

- Module name changed from `sports_py` to `sports`
- `get_match_score()` renamed to `get_match()`
- `get_sport_scores()` renamed to `get_sport()`
- `get_all_matches()` renamed to `all_matches()`
- `get_team_info()` renamed to `get_team()`
- `to_json()` method removed from `Match` objects
- NBA teams can now be accessed through `get_team()`
- Valid sport names can accessed via constant variables (see README for more details)