Documment config.log_formatter added on 51aeae91

[ci skip]
Improve Active View Overview guide. [ci skip]
Merge pull request #11401 from dpdawson/master

Improved Active View Overview guide. [ci skip]
move `MissingHelperError` out of the `ClassMethods` module.
add test-case to verify `error.path` when a helper was not found.

This verifies the code added with:
https://github.com/rails/rails/commit/99c9d18601539c7e7e87f26bb047add1f93072af
Typo fix [skip ci]
Merge pull request #11414 from ankit8898/typo

Typo fix [skip ci]
Removing Gem.source_index [ci skip]
Merge pull request #11417 from arunagw/gem_source_index_no_required

Removing Gem.source_index [ci skip]
Remove update:application_controller rake task.
Merge pull request #11420 from simi/remove_update_application_controller_task

Remove update:application_controller rake task.
Remove block argument from callback example.

[ci skip]
Merge pull request #11413 from envylabs/master

Remove block argument from callback example. [ci skip]
Removed unused file! Moved to actionview

Removed unused file as this has been
moved to actionview
Merge pull request #11421 from arunagw/actionpack_activerecord_remove

Removed unused file! Moved to actionview
Added missing actionview in list for release
Merge pull request #11422 from arunagw/added_missing_actionview

Added missing actionview in list for release
Reset @column_defaults when assigning .
ActionController::Live documentation in the guides.

I'm adding documentation to the action_controller_overview guide which
should tell people how to stream arbitrary data.
it's xml, not json

change docs for xml serializer to talk about xml