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
Frameworks throws AssertionError saying you cannot set required=True and read_only=True on editable=False model fields.  We should not make the field required if editable=False.
Docs whitespace fix.
Remove `filter_backend`.

Closes #1775.
Remove `allow_empty`.

Closes #1774.
Remove `allow_empty`
Remove `pk_url_field`, `slug_url_field`, `slug_field`.

Closes #1773.
Remove `page_size` argument.

`paginate_queryset` no longer takes an optional `page_size` argument.
Remove `.model` usage in tests.

Remove the shortcut `.model` view attribute usage from test cases.
Minor tidy up.
Remove deprecated generic views.

`MultipleObjectAPIView` and `SingleObjectAPIView` are no longer
required.
Remove `.link()` and `.action()` decorators.
`get_paginate_by` no longer takes optional `.queryset`
Remove unused imports.
First pass
Add subclass matching to serializer field mapping.
Traverse the method resolution order when mapping serializer fields.