add an implementation of the MAC token spec

https://datatracker.ietf.org/doc/draft-ietf-oauth-v2-http-mac/
rubocop offenses
Merge pull request #181 from steved555/sdavidovitz/mac

add an implementation of the MAC token spec
Fix RuboCop offenses
Lock rest-client to ~> 1.6.0 on Ruby 1.8.7
Base64.strict_encode64 is not available on Ruby 1.8.7
OAuth 2 is all grown up!
Merge remote-tracking branch 'upstream/master'