Added support for custom AuthenticationSchemes, to be able to test the upcoming Windows Authentication support.
Added support for custom AuthenticationSchemes, to be able to test the upcoming Windows Authentication support.

dyh333/RestSharp,mattleibow/RestSharp,wparad/RestSharp,fmmendo/RestSharp,dgreenbean/RestSharp,haithemaraissia/RestSharp,RestSharp-resurrected/RestSharp,who/RestSharp,mattwalden/RestSharp,wparad/RestSharp,uQr/RestSharp,PKRoma/RestSharp,mwereda/RestSharp,huoxudong125/RestSharp,eamonwoortman/RestSharp.Unity,lydonchandra/RestSharp,restsharp/RestSharp,periface/RestSharp,SaltyDH/RestSharp,jiangzm/RestSharp,felipegtx/RestSharp,amccarter/RestSharp,rivy/RestSharp,chengxiaole/RestSharp,dmgandini/RestSharp,KraigM/RestSharp,benfo/RestSharp,rucila/RestSharp,kouweizhong/RestSharp,cnascimento/RestSharp