Mlb-statsapi

FIX: game_scoring_plays() and game_scoring_play_data() broken due to MLB data change 44

FIX: Add missing startDate and endDate params to teams_stats endpoint config
ENH: Include venue id and name in the schedule return data
NEW: Support warning for Python 2 - Support will be dropped on/after Jan 1, 2021

**FIX**:
* Update required params for team_roster endpoint 29
* Leading & trailing slashes not honored in endpoint config 28

**ENHANCE**:
* Testing 22
* Add requirements.txt files
* Clean up code formatting

Standardize code formatting using black, and add flake8 linter config.