Update documentation to use Oauth2 provider un Rails 2.x

Signed-off-by: Yannick Chaze <yannick@wearecloud.com>
add license information to gemspece

This way it can be used with rubygems.org API
return false for allow? when token is not found
Merged pull requests from https://github.com/pelle/oauth-plugin/pull/132 (OAuth 2 refresh tokens should now work) and https://github.com/pelle/oauth-plugin/pull/137 (allow? will now return false when the token is not found)
Don't try and use client_application if we didn't find it (https://github.com/pelle/oauth-plugin/pull/125)
Added refresh_token accessor
Made the OAuth 2 redirect_uri param in the options hash mandatory and created a method to get it.
Made the access token refresh when necesary. It checks for the expires_in and expires_at timestamps when creating a new ConsumerToken and it gives defaults (3600 seconds, 1 hours) when none are given. It then refreshes the token and updates it in the datastore.
Added fields for expired_at and expired_in to the migration.
I forgot to persist the access token in the process of updating for OAuth 2.0, now fixed (HOW DO YOU FORGET SUCH A THING!?)
Treat rails 4 the same as rails 3
Replace deprecated use of Relation#first with finder options
Replace deprecated filter method in Filter class
Merge pull request #140 from tomhughes/rails4

Rails 4 support
Merge pull request #123 from yann/master

Update documentation for Oauth2 provider in Rails 2.x
Merge pull request #134 from jordimassaguerpla/master

add license information to the gemspec
Merge pull request #137 from thetizzo/master

allow? should return false if no token is found
Merge pull request #139 from RubenHoms/feature/access-token-refresh

OAuth 2.0 functionality and other fixes
Fix specs
Remove deprecation messages