Evaluate content before passing to regex.sub

Issue #1708
evaluate content at function start
remove dep on python_2_unicode_compatible

python_2_unicode_compatible is not available in all Django versions
replace unicode call with force_text
Add subclass matching to serializer field mapping.
Traverse the method resolution order when mapping serializer fields.
Add utility function to match classes in dictionary.
Generator implementation of class mapping.
Added get filename as encoded
 This filename described in RFC 6266
Added test for encoded filename
Removed assert for wrong charset
Removed use encoding available only in py3
Refactor encoded filename feature per #1531
Fix encoded filename parsing to allow for lang
Move parser tests to correct directory
Merge remote-tracking branch 'poswald/view-description-as-promise' into view-description-as-promise
Fix linting issues
Use force_text from compat
Remove unicode strings
Refactor disposition unpacking for clarity