[Testing guide] Use "Fixtures API" instead of "fixture api".
[Testing guide] Using "Fixtures API" consistently

- In guides, "API" is used consistently instead of "api".
- Reason behind replacing "fixtures API" to "Fixtures API" is because
  here we are referring to the concept of "fixtures". In other places in
  the guide "fixture" OR "fixtures" is referred to the single or
  multiple instances of test data.
- This is also followup of https://github.com/rails/docrails/commit/aa9d1332b20305dd860b21a7ada06c5252bebad5#commitcomment-8497376.
Fix grammar on ActiveRecord::AttributeMethods doc.

[ci skip]
allow 'all' for :domain option in addition to :all
Don't remove mailer layouts files
Refactor `add_column_options!`, to move the quoting of default value for :uuid in `quote_value`.
Rename to `quote_default_expression` from `quote_value`
Start Rails 5 development :tada:

We will support only Ruby >= 2.1.

But right now we don't accept pull requests with syntax changes to drop
support to Ruby 1.9.
We don't need to use sass-rails 5.0.0.beta
Remove custom errors page section from the guides

This pattern is too problematic and introduces a lot of edge cases:

  * On 4.2, the issue https://github.com/rails/rails/issues/15124 is
    back again.
  * needs to define each action for each http status otherwise the
    router raises ActionController::RoutingError (No route matches).
  * If the router has `match "/*username",...` and some action is
    missing, Rails will pick up the "match" and try to do its job.
  * encourages people to copy & paste programming. Not DRY.

[ci skip]
Use jquery-rails master to resolve dependencies

delayed_job_active_record doesn't allow Rails 5 yet
Merge pull request #17799 from kamipo/refactor_add_column_options

Refactor `add_column_options!`, to move the quoting of default value for :uuid in `quote_value`.
fixed indent of end in jdom.rb
Merge pull request #17818 from bigtone1284/edits_refactor_cop

fixed indent of end in jdom.rb
Prevent Numeric#to_s from allocating an array
Allow failures with Active Job
Allow failures with Active Job integration tests
Fix Sidekiq ActiveJob integration setup

* .connect on a Redis connection wasn't valid
* Reset logger after we're done testing for redis connection to avoid
  "closed stream" error when starting server for real from a fork
make OR in journey patterns compile to a valid regular expression
[ci skip] fix class name