Documentation with helpers is a bit congested

Right now there is one page "helpers", with both markers and fixtures.

I think it'd be more intuitive for readers if markers and fixtures were split off into their own page. In addition, it'd save a level of section indentation in reStructuredText.

Secondly, if/when marks and fixtures is broke up, it should be done into sections, e.g:

Markers (now its own page)

• Database
  • pytest.mark.django_db
• URLs
  • pytest.mark.urls
• Templates
  • pytest.mark.ignore_template_errors

Fixtures (now its own page)

• Database
  • db
  • transactional_db
• Settings
  • settings
• Server
  • live_server
• RequestFactory
  • rf
  • rf_user #568
  • rf_unauth #568
  • rf_admin #568
• Client
  • client
  • admin_client
  • user_client #568
• User
  • django_username_field
  • django_user_model
  • django_user #568
  • admin_user
• Mail
  • mailoutbox
• Assertions
  • django_assert_num_queries

When I do this, I can also do a general cleanup of this section to make it more maintainable down the road.

Locate the current documentation page titled "helpers" and review how markers and fixtures are organized. Split them into separate pages, reorganize each into the proposed sections, and include the listed helpers; done when the documentation is less indented and the marker and fixture references are complete and maintainable.