Add bittrex Config

[Varunram]

I added the config part, sadly I don't think I have the luxury to write handlers as well. The primary difference between Vertpig and Bittrex is that Bittrex returns floats for suitable values whereas vertpig returns strings. I tested all the public API endpoints and they do work, but further testing is most certainly needed, the functions without handlers need polishing and may have bugs.

I suggest this not be merged - instead someone can work on this to build the handlers instead of spending time again to write the config. I chose to build these because I was handling something related, maybe something similar can happen to someone else too :)