The `DefaultContentNegotiation` handler uses

For example: Google Chrome sends an Accept-header of `Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8`, when I request a *.png URL.
After matching the media-types with the available renderers (in my case only a custom `PNGRenderer` with a `media_type='image/png'`), only `*/*;q=0.8` is left, which happens to have the same length as the "image/png" media-type defined by the renderer (9 characters).

The specificity of the renderer's media-type over the Accept-header's one is only determined by length.
Using your `_MediaType.precedence` would be preferable in my eyes.

Regards, Fabian

Cache all fields per serializer instance

Add widgets for DateField and DateTimeField

Add support for partial serializer updates

http://www.python.org/dev/peps/pep-0008/#programming-recommendations

minor docs fix

http://www.python.org/dev/peps/pep-0008/#programming-recommendations

added RegexField

Conflicts:
	docs/topics/release-notes.md

Serializer method field

Cache default_fields per serializer instance for faster serialization

Fix related serializers with source argument that resolves to a callable