League 2.3 - Challenger and single entry by summoner

Added functions for the two new endpoints:

* by-summoner/{summonerid}/entry - this endpoint displays only the entry for the given summoner. The existing endpoint shows entries for every summoner in the same league
* challenger - challenger tier data for Ranked SoloQ 5s, Ranked Team 3s, and Ranked Team 5s

I have added tests for the new functions as well as some variables to prevent typos