Added endpoints for player tracking to get second spectrum stats.

Changed current season to 2017-18 in constants.py.

I have found 24 endpoints from stats.nba.com that are not currently included in nba_py

Here are first 6 new endpoints in 6 new classes that can hopefully be added to the master repo

I'm quite new to Python and GitHub so please let me know if I'm doing anything wrong, but hopefully I did enough testing on these classes before committing.

Fixed Travis CI suggestions

Added some parameters that aren't required but can be provided anyway

Team hustle stats!

Two new endpoints with their classes:  TeamHustleLeaders (endpoint: leaguehustlestatsteamleaders) and TeamHustleStats (endpoint: leaguehustlestatsteam)

Player hustle stats added!  10 of 24 new endpoints now added (if you include teams.py).

In this update:  Two new endpoints with their classes:  PlayerHustleLeaders (endpoint: leaguehustlestatsplayerleaders) and PlayerHustleStats (endpoint: leaguehustlestatsplayer)

fixed Travis CI whitespace issues and added call to _api_scrape inside TeamHustleStats

Travis CI whitespace issues fixed

Updated functionality