Improve the testing guide [ci skip]

Improve the "Testing Rails Applications" guide adding a section for
testing helpers and a little note about associations with ActiveRecord
and YAML fixtures.

Also add a link to Fixture Builder ; yet another replacement for
fixtures such as Machinist or FactoryGirl.
Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs update [ci skip]
Creating an SSE class to be used with ActionController::Live.
Added Action View in 'rake about' [ci skip]
added String#to_date documentation to Rails 4 upgrade guide

[ci skip]
Removing obsolete html tags in favor of markdown code block.
Revert "Removing obsolete html tags in favor of markdown code block"

This reverts commit 157dc275da0ad38635337b7c1d96de656d91de8e.
Minor align BR tags with HTML void - with reference to the generators code change - https://github.com/rails/rails/commit/f038d4cc5fe1ac21f92c7e32c61ff85a0c816f3f
Add tests for ActiveModel::Serializers::JSON#as_json ordering
Avoid Skip in test, have a unified test for order
Rely on NoMethodError#name when deciding to raise DelegationError.

Different Ruby implementations present backtraces differently, as
it should be an information consumed by humans.
A better implementation should use data from the error, in this case
returned by NoMethodError#name.

Fixes issues with Rubinius, which presents backtraces differently from
MRI.
using assert_not instead of refute
Merge pull request #11868 from rajcybage/fix_refute

using assert_not instead of refute
 #11804: Add description of action in Getting Started Guide

[ci skip]

Closes #11804
Updated outdated initialization guide [ci skip]
Add String#remove(pattern) as a short-hand for the common pattern of String#gsub(pattern, '')
Merge pull request #11847 from AJ-Acevedo/master

Updated outdated initialization guide [ci skip]
Merge pull request #11807 from jetthoughts/11804_actions_are_public_methods

Add description of action in Getting Started Guide [ci skip]
Generate namespaced routes correctly for generators. Fix for #11532
guides should tell people to write ruby code, not output