Fix documentation for group_sequence_provider
document multiple recipients in XML configs

Adds an example on how to configure multiple recipients in Monolog
for sending log entries as e-mails.
Fixed minor typos.
feature #4140 [Cookbook][Logging] document multiple recipients in XML configs (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[Cookbook][Logging] document multiple recipients in XML configs

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/MonologBundle#91)
| Applies to    | all
| Fixed tickets | #3940, #4135

Commits
-------

37ab23d document multiple recipients in XML configs
bug #4145 Fix documentation for group_sequence_provider (giosh94mhz)

This PR was merged into the 2.3 branch.

Discussion
----------

Fix documentation for group_sequence_provider

The current documentation for `group_sequence_provider` option in the docs is wrong.
It states that the option should be set with:
```YAML
Your\Class\Name:
    group_sequence_provider: ~
    ...
````
But this didn't work.

By looking at the unit test I came up the the right version:
```YAML
Your\Class\Name:
    group_sequence_provider: true
    ...
````

Commits
-------

81cec5d Fix documentation for group_sequence_provider
Adding 'attr' option to the Textarea options list

`attr` is a quite useful option, but not yet listed here. BTW, the `attr.rst.inc` file already includes an `attr` conf. example concerning textareas.
minor #4152 Adding 'attr' option to the Textarea options list (ronanguilloux)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4152).

Discussion
----------

Adding 'attr' option to the Textarea options list

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?  | nope
| Applies to    | all?
| Fixed tickets | ?

`attr` is a quite useful option, but not yet listed here, so I added it.
BTW, the `attr.rst.inc` file already includes an `attr` conf. example concerning textareas.

Commits
-------

d6f9bd1 Adding 'attr' option to the Textarea options list
[Reference] consistent & complete config examples
bug #4164 Fixed minor typos. (ahsio)

This PR was merged into the 2.3 branch.

Discussion
----------

Fixed minor typos.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all (or 2.3+)
| Fixed tickets |

Commits
-------

da441ae Fixed minor typos.
minor #4160 [Reference] consistent & complete config examples (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[Reference] consistent & complete config examples

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Make configuration examples in the reference section consistent throughout the different configuration formats. Also fixing several syntax issues.

This follow #4114 and #4129.

Commits
-------

01dc25c [Reference] consistent & complete config examples
Merge branch '2.3' into 2.4

* 2.3:
  [Reference] consistent & complete config examples
  Adding 'attr' option to the Textarea options list
  Fixed minor typos.
  document multiple recipients in XML configs
  Fix documentation for group_sequence_provider

Conflicts:
	components/translation/introduction.rst
	reference/constraints/Callback.rst
	reference/constraints/Image.rst