The `capify` command has been removed by Capistrano 3 and became to
`cap install`.
Therefore, the `capify!` method has no meaning in Capistrano 3.
I think that should deprecate.

Ref: https://github.com/capistrano/capistrano/commit/492793916acf32ffe1604daec6fd4892c8935018

Remove references to deprecared raise_runtime_errors from documentation, which is always enabled now. Ref: https://github.com/rails/sprockets-rails/commit/655b93bffc6f51b96a7cc097f9010942693bfaae and https://github.com/rails/rails/pull/24070 . Fixes #29483 [ci skip] (#29484)

Added a small section for it in the `Active Support Core Extensions`
guide. [ci skip]

Update upgrading guide w.r.t. Parameters to use other example method than slice as this has actually been implemented by Parameters

Commit 1a5d9399 removed the "Profiling Rails Applications" guide
but the YAML entry for this guide wasn't.

[ci skip]

Other examples were removed in 53ff5fc6

[ci skip]

drivers.

When using `driver_by` with capybara-webkit or poltergeist,
SystemTesting::Driver will register the driver while passing
`screen_size` and `options` parameteres.

`options` could contain any option supported by the underlying driver.

[ci skip]

This lists the `assert_changes` and `assert_no_changes` methods in the
guides. [ci skip]

ActionDispatch::Callbacks.to_prepare was removed in #27587
[ci skip]

`gmail` --> `Gmail`

[ci skip]

".. with __dir__ we can restore order in the Universe." - by @fxn

Related to 5b8738c2

This commit changes encrypted cookies from AES in CBC HMAC mode to
Authenticated Encryption using AES-GCM. It also provides a cookie jar
to transparently upgrade encrypted cookies to this new scheme. Some
other notable changes include:

- There is a new application configuration value:
  +use_authenticated_cookie_encryption+. When enabled, AEAD encrypted
  cookies will be used.

- +cookies.signed+ does not raise a +TypeError+ now if the name of an
  encrypted cookie is used. Encrypted cookies using the same key as
  signed cookies would be verified and serialization would then fail
  due the message still be encrypted.

[ci skip]

Telling people about prerequisites, and then telling them a page later
how to check and install those prerequisites, is confusing. This commit
removes the list and just handles the software installation in one
place.

Fixes #28565

When define callbacks latest definition on the same callback/method
overwrites previous ones.

* Nested Model Forms guide is out of date, not linked from index,
  and material is covered in the Form Helpers guide.
* Profiling guide was committed as an outline years ago
  and never actually written.