Add game events XML serializer
Add game events XML serializer to serializer .h
Add game events operation

The game events operation uses a gameID to request the
game_events.xml file from an individual game.
Add game events property
Add game events operation to download method
Add game events operation to batch operations
Add game events to download response
Add method to clean up description attributes
Refactor actions parsing to use clean descriptions
Refactor at bat parsing to use clean descriptions
Add action parsing method
Refactor half inning parsing method
Remove unnecessary at bat / action parsing methods