Making sure the assert does not fail  when required=False, read_only=True

get_excluded_fieldnames() should respect Meta options' ability to be eit...

get_excluded_fieldnames() should respect Meta options' ability to be either a tuple or list. Fixes #490.
Refactored `if self.opt.fields` out of the for loop.
Updated and cleaned up the validation-tests.

When incorrect parameters are supplied to the obtain auth token view
400 *is* the correct response.

Call model's .full_clean() method, eg. to validate uniqueness

fixed #469 - RegexField <--> BrowsableAPI Bug

Fix for #460 

Add support for "true" and "false" as BooleanField values 

ModelSerializer traverse related

Textual tutorial fixes

Plural/singular fix.
Typo fixed.

Added a sentence introducing the second view.
Fix one or two additional sentences.

@permission_classes takes a tuple or list.

Some singular/plural fixes.
Fixed some 'serialise->serialize' kind of UK/US differences. The 'z' seems more common in the rest of the docs, so that's what I used.
Removed a half-finished-sentence left dangling somewhere.