Add `config.active_record.warn_on_records_fetched_greater_than` to the
Configuring Rails Guide.

Fixes db:structure:dump when using schema_search_path and PostgreSQL
extensions.

Closes #17157.

* Fix a few typos
* Wrap some lines around 80 chars
* Rephrase some statements

[ci skip]

Serving public files from multiple paths was removed in
afc82882

Deprecate `required` option in favor of `optional` for belongs_to.

* "rm docs for dependency_loading and disable_dependency_loading config"

It was added back in a71350ca by @tenderlove

See also #13142

removes docs for dependency_loading config option and disable_dependency_loading initializer because it was removed by commit a8bf1297

- Changed `IN` to `ON` in all note sentences in guides.

Closes https://github.com/rails/rails/issues/18372

[ci skip]

This stems from [a comment](rails#17227 (comment)) by @dhh.
In summary:

* New Rails 5.0 apps will not accept `return false` as a way to halt callback chains, and will not display a deprecation warning.
* Existing apps ported to Rails 5.0 will still accept `return false` as a way to halt callback chains, albeit with a deprecation warning.

For this purpose, this commit introduces a Rails configuration option:

```ruby
config.active_support.halt_callback_chains_on_return_false
```

For new Rails 5.0 apps, this option will be set to `false` by a new initializer
`config/initializers/callback_terminator.rb`:

```ruby
Rails.application.config.active_support.halt_callback_chains_on_return_false = false
```

For existing apps ported to Rails 5.0, the initializers above will not exist.
Even running `rake rails:update` will not create this initializer.

Since the default value of `halt_callback_chains_on_return_false` is set to
`true`, these apps will still accept `return true` as a way to halt callback
chains, displaying a deprecation warning.

Developers will be able to switch to the new behavior (and stop the warning)
by manually adding the line above to their `config/application.rb`.

A gist with the suggested release notes to add to Rails 5.0 after this
commit is available at https://gist.github.com/claudiob/614c59409fb7d11f2931

This config setting has been available for quite a while but was not
documented.

References #18148.

Allow static asset serving from env variable (enhanced!)
Conflicts:
	railties/CHANGELOG.md

Reason: There is a wrong newline, a typo, and the change
to singular is not good.

This reverts commit d76380cf.

 * Change 'Any ***s that are...' to 'Any *** that is...'
 * Fix style for default rescue_responses setting

This is a follow-up commit to:

 * https://github.com/rails/rails/pull/17076
 * https://github.com/yuki24/rails/commit/89b8836f2470c689f6b7d52cab3a418bb63aef26

[ci skip]

Goals:

1. Default to :random for newly generated applications
2. Default to :sorted for existing applications with a warning
3. Only show the warning once
4. Only show the warning if the app actually uses AS::TestCase

Fixes #16769

I found an * does not work in Markdown notation. It should be removed.

`ActiveSupport::Logger` has no concept like auto flushing since it has no userspace buffering.
It's a remnant of `ActiveSupport::BufferedLogger` epoch which was since removed from rails.

Remove ActiveRecord config instructions for active_record.attribute_types_cached_by_default, which was removed in https://github.com/rails/rails/commit/66736c8e50585

This reverts commit de489134.

Conflicts:
	railties/lib/rails/railtie/configuration.rb

It added regression. Will be back after the beta

1. Hashes can be assigned
2. We don't need a special level anymore

The method chain only works in the top level.

If users need a second level they need to assign a OrderedOptions to the
key:

    config.resque.server = ActiveSupport::OrderedOptions.new
    config.resque.server.url = "http://localhost"
    config.resque.server.port = 3000

[Rafael Mendonça França + Carlos Antonio da Silva]