During the `5.0.0.beta1` release, the CHANGELOGs got an entry like the
following:

```
* No changes.
```

It is kinda confusing as there are indeed changes after it. Not a
biggie, just a small pass over the CHANGELOGs.

[ci skip]

This reverts commit 65a61ab7, reversing
changes made to 14314ca1.

This PR broke the build

`config.force_ssl = true` will set
config.action_mailer.default_url_options = { protocol: 'https' }

If you have turned on force_ssl, and then gone to the effort of setting
config.action_mailer.default_url_options = {host: 'example.com'} then
you are probably pointing people back to your current app and want
https on that too.

This reverts commit f2a8c236, reversing
changes made to 3046c9bb.

When #deliver_now is called all translations within the
generated email will be looked up for the current I18n
locale.

    I18n.locale = ‘de’
    mail.deliver_now # Generates german email, correct

In #enqueue_delivery the locale was not considered and
the resulting job uses the default locale.

    I18n.locale = ‘de’
    mail.deliver_later # Generate english email, incorrect

In order to achieve a consistent behaviour the current locale
is now always passed to `ActionMailer::DeliveryJob`.

Also add a CHANGELOG entry for #18587

[ci skip]

Use a preview interceptor to search for inline cid: urls in src
attributes and convert them to data urls.

Mailer preview now uses `url_for` to fix links to emails for apps running on a subdirectory, closes #19092.

While this was true before when every `dd` had a value,
this patch makes sure that everything keeps lining up even
when the `dd` node is blank.

One or multiple mail interceptors can be unregistered using
`ActionMailer::Base.unregister_interceptors` or
`ActionMailer::Base.unregister_interceptor`.

For preview interceptors, it's possible to use
`ActionMailer::Base.unregister_preview_interceptors` or
`ActionMailer::Base.unregister_preview_interceptor`.

Refactors logic to constantize a string/symbol into separate method.

Following the same naming convention used in
controllers and jobs.

These methods were deprecated in Rails 4.2 (see f4ee1147) so they can
be safely removed in Rails 5.0.

Given the following templates:

    mailer/demo.html.erb
    mailer/demo.en.html.erb
    mailer/demo.pt.html.erb

Before this change for a locale that doesn't have its related file
the `mailer/demo.html.erb` will
be rendered even if `en` is the default locale.

Now `mailer/demo.en.html.erb` has precedence over the file without
 locale.

Also, it is possible to give a fallback.

    mailer/demo.pt.html.erb
    mailer/demo.pt-BR.html.erb

So if the locale is `pt-PT`, `mailer/demo.pt.html.erb` will be
 rendered given the right I18n fallback configuration.

Fixes #11884.

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.

[skip ci]

[skip ci]

Email does not support relative links since there is no implicit host. Therefore all links inside of emails must be fully qualified URLs. All path helpers are now deprecated. When removed, the error will give early indication to developers to use `*_url` methods instead.

Currently if a developer uses a `*_path` helper, their tests and `mail_view` will not catch the mistake. The only way to see the error is by sending emails in production. Preventing sending out emails with non-working path's is the desired end goal of this PR.

Currently path helpers are mixed-in to controllers (the ActionMailer::Base acts as a controller). All `*_url` and `*_path` helpers are made available through the same module. This PR separates this behavior into two modules so we can extend the `*_path` methods to add a Deprecation to them. Once deprecated we can use this same area to raise a NoMethodError and add an informative message directing the developer to use `*_url` instead.

The module with warnings is only mixed in when a controller returns false from the newly added `supports_relative_path?`.

Paired @sgrif & @schneems

Closes #16163

Adding attachments after a call to `mail` will result in invalid emails.
This is related to the fact, that `mail` is making the required preparations
before the email is ready to be sent. These change depending on your
added attachments.

Adds `config.action_mailer.preview_enabled`

This allows mail previewing to be enabled easily in non-development
environments such as staging. The default is set to true for development
so no changes should be required to existing Rails applications.

The mail preview path can still be configured using the existing
`config.action_mailer.preview_path` configuration option.

Adding this avoids devs from having to do stuff like:
https://gist.github.com/lengarvey/fa2c9bd6cdbeba96526a

Update actionmailer/CHANGELOG with new configuration.
Update configuring guide with new configuratation.
Add `config.action_mailer.preview_path` to configuring guide.

This was partially broken because `preview_interceptors=` just assigned the
raw values, whithout going through `register_preview_interceptor`. Now the
Action Mailer railtie takes care of the `preview_interceptors` option.

This commit is a partial revert of:

Revert "Merge pull request #15739 from y-yagi/correct_doc_for_action_mailer_base"

This reverts commit a15704d7, reversing
changes made to 1bd12a86.

/cc @kuldeepaggarwal @y-yagi

Remove 4-1 related entries from master [ci skip]