Fix doc for custom exception sample

The way to provide a default detail for APIException is to define a `default_detail` attribute on the subclass.

Defining a `detail` attribute without `default_detail` will not work, and will result in empty detail instead.
Merge pull request #1379 from bodylabs/exception_example

Fix doc for custom exception sample
Update fields.md
Merge pull request #1381 from meoooh/master

just little bit modify
fixed typo (wrong "its")
Merge pull request #1383 from jfw/patch-1

fixed typo (wrong "its")
Viewsets docs typo

The docstring in the example said "update" instead of "create".
Merge pull request #1384 from meshy/patch-1

Viewsets docs typo
Fixes typo (Implicit instead of Implict).
Merge pull request #1385 from juroe/master

Fixes typo (Implicit instead of Implict).
Fixed a bug backticks

fix

    you may optionally exclude the ``self.check_object_permissions, and simply return the object from the `get_object_or_404` lookup.

to

    you may optionally exclude the `self.check_object_permissions`, and simply return the object from the `get_object_or_404` lookup.
Merge pull request #1387 from RicterZ/patch-1

Fixed a bug backticks
Generate random token directly
Merge pull request #1382 from mking/use-urandom-directly

Generate random token directly