Reorganize file to separate public API.
Move __init__.py -> djqscsv.py

so that __init__.py can import the public functions
Fix reference to non-existent variable
Correct Content-Disposition header

fixes #2 on github
Test if qs is ValuesQuerySet before calling values

A nasty effect of .values() in django is that if you call values('field1', 'field2'), you will get a ValuesQuerySet with only those fields. However, if you call values *again* on that qs without args, it will give you values for all fields in the model. This is bad for calling functions that assume by sending a stripped-down values queryset, they can solve the security problem of what fields to export. With this fix, they can as expected.
Fix missing reference
Fix incorrect reference in package init
Add cache control to response
wip. initial commit of test suite