adding OSX section and adding .DS_Store
previously the code was checking to see if Invoice

had `USERNAME_FIELD` which it doesn't. I have updated it to
check the user model which is the intended behaviour.
adding @myusuf3 to authors
Merge pull request #109 from myusuf3/customer-user-fix

Customer User Fix
updating the documentation to take advantage of

method_decorator and using decorators with the dispatch
function of Class-Based views.
Merge pull request #110 from pydanny/class-based-view-docs

updating the documentation to take advantage of