Documents add and remove convenience methods
Changed user_has examples for consistency with ability example
Merge branch 'dev'
Updates version number
Refactor tests to use assertItemsEqual instead of sets
Refactors roles relationship to use association proxy
Refactors for association proxy
Removes twill requirement
Allows external for pip install
Allows external twill
Allows external and unverified for twill
Sets up joined table inheritence