Fixed json_escape (again)

Expanded test coverage for html_escape and json_escape

removed duplicate test case

remove nil in NullType#ref.

Return Nil is implicit in a method and this syntax is used in the others
classes

Formatting, capitalization, and punctuation fixes [ci skip]

Second try on this commit.

TextHelper#simple_format attempts to call undefined raw method

Fix AR#method_missing re-dispatching into overwritten attribute methods

Conflicts:
	activerecord/lib/active_record/attribute_methods.rb

Now users have to explicit mark the unit as safe if they trust it.

Closes #13161

Conflicts:
	actionpack/lib/action_view/helpers/number_helper.rb
	actionpack/test/template/number_helper_i18n_test.rb

Follow up to #12958.

Install Spring preloader when generating new applications

Added JSON related items to the 4.1 release notes

Avoid one-liner conditionals when they are too big. Avoid concatenating
strings to build error messages. Improve messages a bit.

Action Pack Variants

By default, variants in the templates will be picked up if a variant is set
and there's a match. The format will be:

  app/views/projects/show.html.erb
  app/views/projects/show.html+tablet.erb
  app/views/projects/show.html+phone.erb

If request.variant = :tablet is set, we'll automatically be rendering the
html+tablet template.

In the controller, we can also tailer to the variants with this syntax:

  class ProjectsController < ActionController::Base
    def show
      respond_to do |format|
        format.html do |html|
          @stars = @project.stars

          html.tablet { @notifications = @project.notifications }
          html.phone  { @chat_heads    = @project.chat_heads }
        end

        format.js
        format.atom
      end
    end
  end

The variant itself is nil by default, but can be set in before filters, like
so:

  class ApplicationController < ActionController::Base
    before_action do
      if request.user_agent =~ /iPad/
        request.variant = :tablet
      end
    end
  end

This is modeled loosely on custom mime types, but it's specifically not
intended to be used together. If you're going to make a custom mime type,
you don't need a variant. Variants are for variations on a single mime
types.

This reads a lot better, and we won't need to try start_with? for blank
delimiters.

Also rename method name to read better.

The conversion without area code already changed the passed number in
place, so change the other method to do the same.