fix 'method redefined' warnings

Fix a typo

Replace `a` with `an`

This reverts commit 8c3cca5e, reversing
changes made to 9dcf67c4.

Reason: https://github.com/rails/rails/pull/23562#issuecomment-181442569

Update rails-html-sanitizer version to  v1.0.3

rails-html-sanitizer 1.0.2 is vulnerable: https://groups.google.com/d/msg/rubyonrails-security/uh--W4TDwmI/m_CVZtdbFQAJ

Remove references to Rails 4 from assets guide [ci skip]

revert dev:cache to rake task, fixes #23410

Add numeric type in the doc [ci skip]

Follow up to #23508.

remove `faye-websocket` dependency from README [ci skip]

`faye-websocket` gem is no longer used from 322dca29.

config examples for ActionCable now use Rails.application.config.action_cable

update turbolinks url [ci skip]

`schema_type` returns symbol rather than string

Some existing examples used ActionCable.server.config but for
configuring allowed_request_origins that is overridden in development
mode. The correct place to set that is
Rails.application.config.action_cable which the ActionCable initializer
loads from. I thought the other two examples should be changed as well
just in case a default value that would override a configured value is
introduced for either log_tags or disable_request_forgery_protection in
the future.

Added numeric helper into `SchemaStatements` for MySQL and PostgreSQL

doc changes to clarify asset pipeline

for rails/rails#23431

       modified:   guides/source/asset_pipeline.md
* description of asset combination from apps and gems, e.g. jquery-rails
* after @vipulnsward's related change rails/rails#23479
  correction: --skip-sprockets will prevent all of these gems, not just sass-rails and uglifier

       modified:   guides/source/working_with_javascript_in_rails.md
* noted that rails.js requires the asset pipeline

[ci skip]

Hand off the interlock to the new thread in AC::Live

A return value of `schema_type` is used by:

1. primary key type: using as `symbol.inspect`
2. normal column type: using as `symbol.to_s`

It is better to return symbol.

A full write-preferring wait can lead to deadlock.

Publish guide on "Using Rails for API-only Applications"

Fixes #23322
[ci skip]

[ci skip]

With this addition, you can add a column into the table like:

```
  create_table(:numeric_types) do |t|
    t.numeric :foo, precision: 10, scale: 2, default: 2.0
  end
```

The result of the migration above is same with:

```
  create_table(:numeric_types) do |t|
    t.decimal :foo, precision: 10, scale: 2, default: 2.0
  end
```

fix typo in `assert_enqueued_jobs` example [ci skip]

Most importantly, the original request thread must yield its share lock
while waiting for the live thread to commit -- otherwise a request's
base and live threads can deadlock against each other.