Fix AS::NumberHelper results with rationals

:precision was incorrectly being applied to Rationals

before:
  ActiveSupport::NumberHelper.number_to_rounded Rational(10, 3), precision: 2
  => "3.3"
after:
  ActiveSupport::NumberHelper.number_to_rounded Rational(10, 3), precision: 2
  => "3.33"
Update documentation to reflect unsubscription with name.
Avoid looping through subscribers when unsubscribing with a subscriber object.
Feature requests should be made on the mailing list, not submitted to
the issue tracker. See also #15455 [ci skip]
pg, inline casting methods into `OID::Type` objects.

This inlines casting for the most obvious types. The rest will
follow eventually. I need to put some tests in place, to make sure
that the inlining is not causing regressions.

/cc @sgrif
test pg, add basic test cases for point datatype.
docs, fix typo [ci skip]
Merge pull request #15464 from tgxworld/improve_notifications_logic

Improvements to ActiveSupport::Notifications.
Merge pull request #15379 from xuanxu/rational_precision

Fix AS::NumberHelper results with rationals
just use `assert`
File.exist? instead of File.exists? in bin/setup

File.exists? is deprecated in Ruby 2.1+

https://github.com/ruby/ruby/blob/v2_1_2/file.c#L1413
Add missing colon to internal
Remove unused `initialize_attributes` method

This was previously a hook for a special case related to `serialize`,
which has since been removed.
Merge pull request #15473 from sgrif/sg-missing-colon

Add missing colon to internal [ci skip]
Merge pull request #15474 from unixmonkey/master

File.exist? instead of File.exists? in bin/setup
Fix typo in ActionController Overview

* Should say "sensitive" instead of "sensible"
Merge pull request #15477 from aripollak/actioncontroller-overview-typo

Fix typo in ActionController Overview
concat is a hotspot (via AV#append=), so just directly define the methods
Merge pull request #15475 from sgrif/sg-initialize-attributes

Remove unused `initialize_attributes` method
reduce AS::SafeBuffer allocations

html_escape_interpolated_argument is only used in mutation methods:

  https://github.com/rails/rails/blob/c07d09559ec171e1904b55c7ad7e8c7d586ca51b/activesupport/lib/active_support/core_ext/string/output_safety.rb#L174
  https://github.com/rails/rails/blob/c07d09559ec171e1904b55c7ad7e8c7d586ca51b/activesupport/lib/active_support/core_ext/string/output_safety.rb#L179

The return value doesn't need to be converted to an AS::SafeBuffer since
we know that the current object is an AS::SafeBuffer and will be
mutated, and the return value from html_escape_interpolated_argument
will be thrown away