First stab at rails 3.2.x compatibility

- ActionController::Session::AbstractStore is now ActionDispatch::Session::AbstractStore in rails 3
- #set_session method is now passed the rack session options as a fourth parameter
Merge branch 'master' into rails-3.2-compatibility
Update readme for rails 3.x configuration
Remove 'secret' option from docs - no longer part of rails session config
Update gemspec with renamed test file
set_session method now returns the session's id

- Rails 3.2.x depends on rack ~1.4.5, which requires that the session store's #set_session method return the session_id upon successful saving
Add myself to authors file :)
Merge pull request #8 from modcloth/rails-3.2-compatibility

Rails 3.2.x compatibility