Fix failing redirection specs

OAuth2 redirections specs were failing due to order of params.
Fix credentials regex for Mongoid
Fix credentials regex for MongoMapper
Add edge case tests for Mongoid and MongoMapper
Fix failing tests
Merge pull request #506 from arnvald/fix_failing_redirection_specs

Fix failing redirection specs
Merge pull request #468 from weimeng/fix-credentials-regex

Fix #433 credential_regex not escaping special characters for Mongoid & MongoMapper
Clear password confirmation attribute if defined
Make current_user method return nil when user not found
Merge pull request #508 from arnvald/clear-password-confirmation

Clear password confirmation attribute if defined
properly memoize current_user, even if nil
update changelog
login test helpers integration test support
Update integrations tests

* http_method was added to both login_user and logout_user helpers
* parameter name depends on name of user name attribute
fix datamapper specs for password_confirmation
Merge pull request #516 from arnvald/fix-datamapper-tests

fix datamapper specs for password_confirmation
Make login_from session return nil instead of false

This method is not in public API, it's protected, but should
behave consistently anyway.
update supported ORMs and providers in readme
Merge pull request #509 from arnvald/current-user-returns-nil

Make current_user method return nil when user not found
Fix wrong mongomapper save! behaviour

Mongomapper's save! method was overriden to call save, which resulted
in errors not being raised when object was invalid.
Mongomapper supports save! method, however it accepts only :safe option,
it does not work with validate: false, so this option needs to be removed.

Fixes issue #151