Add i18n caveat to number_to_currency docs [ci skip]

I've worked on a few applications that have gone through the
internationalization process and had issues because they were using
`number_to_currency`. The minute a user is allowed to change their
locale, they can change the price displayed on a page from 10 US dollars
to 10 Mexican Pesos, which is far from the same amount of money.

Unlike other helpers that rely on i18n, `number_to_currency` does not
produce equivalent results when the locale is changed.

As I've explained this to a few groups of developers now, I thought it
might make for a good caveat in the docs.

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Fix typos in Rails 5.0 release notes [ci skip]

Fix Regression in Numericality Validations

Fix letter case and grammar in Routing guide

A regression (#22744) introduced in 7500daec caused certain numericality
validations to raise an error when run against an attribute with a
string value. Previously, these validations would successfully run
against string values because the value was cast to a numeric class.

This commit resolves the regression by converting string values to
floats before performing numericality comparison validations.

[fixes #22744]

Covers Regressions:

* <=
* <
* ==
* >
* >=
* other than

`join_to_delete` is same as `join_to_update`

Add #== back to ActionDispatch::MiddlewareStack::Middleware

Add support for passing flags to MySQL2 adapter by array

seeds.rb.tt: fix English.

fixes typo in 5.0 release notes

remove cors initializer from rails app

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Mounting it as prescribed here:

https://github.com/rails/rails/blob/0d1d50c2db40ea1a9d3bebfb0c35da43bbd4d27f/railties/lib/rails/generators/rails/app/templates/config/routes.rb#L5

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`rack-cors` gem is defined in Gemfile by default only if the api,
not defined by default in rails app.

xref #22701.
xref #20612.

[WIP] Rails 5 release notes [ci skip]

use `bin/test` in plugins guide [ci skip]

do not use `div_for` in example [ci skip]

remove content_tag_for example

Fix .keep file issue with ActionCable