Add Code Climate badge to README
Update GemSpec et al to work with Bundler / Ruby 1.9+
Convert Test::Unit to RSpec
Make SessionController more intelligent

* Determine the session class from the name of this controller
* Determine `param_key` from the session class for this controller
Move ORM-specific code out of SimplestAuth::Model

Instead of mixing in `SimplestAuth::Model`, users can now mix in the
appropriate module for the ORM they are using in their application.
Remove `instance_eval` and refactor authentication

Changed the `authenticate_by` method to set the attribute used for
finding the matching user instead of having it redefine the entire
method.  Also removed duplication across the 3 ORM classes.
Allow for different users to be authenticated

Changed the generic `current_user`-related methods to be dynamically
generated by a call to `track_authenticated` after including the module
in the controller.
Remove unused exception classes
Fix return value for `current_*` dynamic methods

This was previously returning `false` instead of `nil` presumably to
ensure that that memoization inside the `current_user` method would
function properly.  I switched this to check that the instance variable
is defined in order to both return `nil` and have memoization function
correctly.  I also updated the instance variable names to reflect the
user types, preventing a bug with caching an incorrect user.
Remove RVM config
Allow sessions to handle different methods of authentication

The previous session-related classes incorrectly assumed that authentication was
happening via an email / password combination.  This commit allows that
behavior to be configured on a per- `Session` and `SessionController`
basis through the use of `Session.authentication_identifier` and
`SessionsController.persist_authenticated`.  Note that this is a
temporary change to implement this configuration, I hope to do away with
this in future versions.
Use `class_attribute` to track user types

Since class instance variables don't propagate down the inheritance
chain, the `logged_in?` method would blow up when checking to see if any
of the registered user types were logged in.
Expose a `login_url` method for redirection
Locks verison of 'activerecord' to be at least 4
Adds 'I18n' for overriding user facing messages.
Adds gem's locale file to I18n load_path
Provide callback to perform post-sign in actions
Make rails-4 branch compatible with rails 3
Add Appraisals for each ORM to run under travis CI
Add travis-ci build status to readme