added an oauth class that lets one get an access_token if they desire through the mirror-api.

takes the args:

client_id
client_secret
refresh_token

it has the method get_access_token to grab a fresh token for api usage.
adding oauth_spec to the spec helper
a spec for the OAuth class
fixture for the oauth response
Created a spec for the OAuth class to test get_access_token.
bumped version
Merge pull request #32 from ciberch/acces-token-creation-issue-19

Access token creation issue 19 - nice