Use Minitest 5.0 syntax for tests
Re-write API and mix-in HTTParty.

Since the API is re-written and not backward-compatible, it should be a
major version increase according to Semantic Versioning standards. But
I think this gem is a bit too young for a 1.X version.
Refactor method definitions to use define_method.

Also remove old commented (unused) code.
Support MtGox with new crypto_ticker API

Comment Vircurex and Bitstamp logic. Add tests for MtGox.
Remove extra stuff from tests
Clean up some unused/commented code
Update README
Update CHANGELOG