Change serializers.Field to serializers.ReadOnlyField for 3.x compatibility

Using this code snippet as-is on DRF 3.0.1 results in a NotImplementedError
being raised for to_representation due to 3.0's changed behavior with
serializers.Field. The code snippet should be updated to use
serializers.ReadOnlyField instead.

Further discussion here:
https://groups.google.com/forum/?fromgroups=#!topic/django-rest-framework/aX8mLT_v3yc

Better errors when serializer has incorrectly named field.

Improve error checking for nested writes.

documentation typo

base-name -> base_name

`Client.logout()` also clears any `force_authenticate`

Update CharField default min_length message.

Release notes & version 3.0.1

Add link to the issues
Fix the milestone link

Hyperlinked PK optimization.

Syntax highlighting

Moved images referenced by the markdown back to the docs directory
Deleted unused image autocomplete.png

Update serializers.py