Add rake test description

No behavior change
Simplify code in AS json encoder
replace regexp global in #url_for
Fix file name in document [ci skip]

This file was renamed in c8a25386d.
Fixing the examples for button_to

The examples do not generate the output they intend to due to not explicitly declaring the hash separations. This causes it to be treated as one parameter instead of the intended two parameters.
Change Class#subclasses doc example
Add ActiveRecord.count documentation when used on group relations
Add documentation for ActiveRecord.select when use strings as arguments
Add example for ActiveRecord::Base.group using a string as argument
Add example for ActiveRecord::Base.joins using a string as argument
Validations guide: validates_with init clarification.

As discussed with @josevalim on Ruby Rogues Parley.
Clarify ActiveModel::Validator initialization in docs.

As discussed with @josevalim on Ruby Rogues Parley.
Fix CoffeeScript example

`a[data-color]` is not used in example html.
Fix supported ruby version for Rails 4
Improve img alt attribute for screen readers

Currently, the img_alt method in ActionView keeps underscores
in the alt attribute. Because underscores are pronounced in
Apple's VoiceOver Utility, this has serious implications for
accessibility. This patch makes underscored or hyphenated file
names (both common in projects) read more naturally in screen
readers by replacing them with spaces. See method documentation
for details.

Added documentation to image_alt method
Supress warning about method redifinition

In i18n gem, the following methods are defined.
- `Hash#except`
- `Hash#slice`

But if there are defined already, i18n skips these definitions.
So these definition by `active_support` are required before `require 'i18n'`.
Merge pull request #9240 from tricknotes/supress-warning

Supress warning about method redifinition
fix a typo on the engine guide
Merge pull request #9245 from vasconcelloslf/fix_guide_typo

fix a typo on the engine guide
fixing bit string test