Rspec 3

Tentative pull request for upgrading to RSpec 3 compatibility.

Right now all deprecations are removed. One big thing we lost was the file_path and location [here](https://github.com/zipmark/rspec_api_documentation/commit/9803e1fa13816045bbeefa8fd2bf2c356d746ff1#diff-e45803a9c6384ad917f1be30b3214164L15). I'd really like to try and get that back before merging this in.