region specific domains

Added support for region specific domains (see https://developer.riotgames.com/discussion/riot-games-api/show/IH27EK1I) via sprintf. 

Unit tests are all passing except RegionTest#testGetDomainDefault because there is no default domain anymore. One option would be to check if region is valid and default to na.api.pvp.net if not.

regards,
danijoo