Update asset_pipeline.md [ci skip]

Just a slight refactor that delegates file sending to the response
object.  This gives us the advantage that if a webserver (in the future)
provides a response object that knows how to do accelerated file
serving, it can implement this method.

No need to declare ActiveRecord::Attributes::Type

Change "parse_query" to "parse_nested_query"

[ci skip]

Add ability to translate rails guides documents.yaml

Some translations of rails guides has their own documents.yaml, for example

Japanese:
https://github.com/yasslab/railsguides.jp/blob/japanese/guides/source/documents.yaml

Traditional Chinese:
https://github.com/docrails-tw/guides/blob/master/rails_guides/helpers.rb#L21,L27
https://github.com/docrails-tw/guides/blob/master/source/documents_zh-TW.yaml

The [Translating Rails Guides](https://github.com/rails/docrails/wiki/translating-rails-guides) says

> Copy the contents of guides/source into your own language directory and translate them.

So that sounds ok to copy guides/source/documents.yaml into language
specific directly and translating them like other markdown files.

Fixed serializing `:at` option for `assert_eqnueued_with` and `assert_performed_with`

Skip _select! call unless needed for preloader

Add more info on working with postgres ENUM type

Remove check for caller_locations in Rails::Engine

Docs: Update options for add_reference

ActiveJob - log enqueued message only after the job was successfully enqueued

action mailer test cases protected method can be `# :nodoc:` [ci skip]

[ci skip] Fix ActiveRecord::Relation#update documentation

[ci skip] Fix #seconds_since_midnight documentation output it will al…

[ci skip] Fix #seconds_since_midnight documentation output it will always return floating pointnumber

* before

```
people = Person.where(group: 'expert')
people.update(group: 'masters')

Note: Updating a large number of records will run a
UPDATE query for each record, which may cause a performance
issue. So if it is not needed to run callbacks for each update, it is
preferred to use <tt>update_all</tt> for updating all records using
a single query.
```

* after

```
people = Person.where(group: 'expert')
people.update(group: 'masters')
```
Note: Updating a large number of records will run an
UPDATE query for each record, which may cause a performance
issue. So if it is not needed to run callbacks for each update, it is
preferred to use <tt>update_all</tt> for updating all records using
a single query.

Update text on CSS Injection

Fix Time.now format in documentation [ci skip]

Use #current instead of #now to prevent zone issues and use new ruby …

Suppress warnings of `assigned but unused variable`

Introduce `Headers#add`. Move `Response#add_header` upstream.

* Introduce `ActionDispatch::Http::Headers#add` to add a value to
  a multivalued header.
* Move `Response#add_header` upstream: https://github.com/rack/rack/pull/957
* Match upstream `Response#have_header?` -> `#has_header?` name change.

YAGNI concurrent-ruby master branch now that 1.0.0.pre3 is released with fixes for warnings and circular require

This reverts commit 37423e4f.

Jeremy is right that we shouldn't remove this.  The fact is that many
engines are depending on this middleware to be in the default stack.
This ties our hands and forces us to keep the middleware in the stack so
that engines will work.  To be extremely clear, I think this is another
smell of "the rack stack" that we have in place.  When manipulating
middleware, we should have meaningful names for places in the req / res
lifecycle **not** have engines depend on a particular constant be in a
particular place in the stack.  This is a weakness of the API that we
have to figure out a way to address before removing the constant.

As far as timing attacks are concerned, we can reduce the granularity
such that it isn't useful information for hackers, but is still useful
for developers.

Wrong usage of 'a' in docs fixed [ci skip]

Add Singleton in NullMutationTracker class

Fixed deprecated string to specify the middleware [ci skip]