Fix League API for players with multiple leagues.

Replace is_int with filter_var since some APIs will return summoner id's as strings.
Merge pull request #9 from Gabrola/dev/fixleague

Fix League API for players with multiple leagues
Refactored the location of all exceptions
Updated exception tests
Added ChampionList DTO to be consistent with the API
Added RecentGames DTO to be consistent
Added a new test for the league api
Updated the Stats DTO to be consistent
Updated the README
Merge branch 'master' into dev/0.5.0
Added an AbstractListDto object
Updated standard DTO lists and added tests
Merge branch 'master' into dev/0.5.0
Added AbstractListDto to static data DTO
Added AbstractListDto documentation
Merge branch 'dev/0.5.0'
Version 0.5.0