Add additional passthrough authorization options and tests

As eluded to in #8, I added additional authorization helpers to pass through to the `faraday` gem. I added `token_auth` and `authorization`, which correlate directly to the methods [as found in faraday](https://github.com/lostisland/faraday/blob/master/lib/faraday/connection.rb).

I added tests for these methods in similar style as the existing tests, which all pass.

Including more than one type of authentication option is not supported for obvious reasons, but if more than 1 is specified, `authorization` takes priority, then `token_auth`, then `basic_auth` due to the nature of the ordering of the `if` statements in the code.