FIX BaseSerializer.from_native has an altered signature

Fix bugfix note

* base classes define it with one parameter
* BaseSerializer currently defines a second parameter, which we make optional here for method-dispatch passivity

FIx link to tox

This fixes a bugfix note that was added because of #1293, which
pointed out that a change in a bugfix [1] broke backwards
compatibility.  The bugfix did not work as expected because a
variable was quoted when it should not have been.  This removes
the quotes around the variable, which brings back the expected
functionality.

saving nested generic relation serializers broken in django 1.6

Simplified some examples in tutorial

This reverts commit d6806340.

get_full_path returns unicode, so we use build_absolute_uri which
returns iri_to_uri'ed one

When many tab's are open (which is necessary for DRF's documentation), it becomes impossible to determine which tab contains which pieces of documentation.  That they are all related is obvious by the use of a common icon, just not the specific page each tab is loaded to.

This change inverts the order of the title to maintain as much useful context as possible on the tabbar.

Simplified some functions in permissions.py

Should it be that way?

djangorestframework-camel-case in docs

sections of the docs for both parsers and renderers.

Added missing custom validation method test