Fixed small typo in docs

ModelSerializer.restore_object - wrap ValueError error in a list

When a ValueError is raised in ModelSerializer.restore_object, the error
is set to a one-element list, rather than a bare string.

Refactor JSONRenderer slightly for easier overriding

docs: add reference to gis serializer

docs: add reference to DRF-gis in fields

added reference to GeoFeatureModelSerializer of django-rest-framework-gis

added django-rest-framework-gis to third party packages section in /docs/api-guide/fields.md

Updated links to Bootstrap components

The previous links landed on the the main page and no longer directly linked to specific areas.

Include query parameter override instructions for OrderingFilter

I added a brief description of how you could specify a different query parameter for the OrderingFilter.

minor doc fix, @api_view() needs an iterable

Fix style for some text

Remove duplicate class attributes

These duplicate attributes are ignored by at least Firefox and Chrome, so this change has no effect on the style