use AUTH_USER_MODULE instead of get_user_model()

This will remove some import loops
fix #19, remove password from the error message
change test settings structure
remove unnecessary mock
fix typos
add django 1.6 to travis
add python 3 to travis config
use string.ascii_letters instead of string.letters
remove django 1.4 from travis config
use range instead of xrange
remove python 3.4 from travis config
add python version classifiers
add license to setup.py
bump version number to 0.7.0
add config for wheel and twine
refactor runtests file

it will now only run django-nopasswords tests
refactor custom user compatability
add django 1.7 beta to travis config
pep8
use hashlib to generate login code