removed observer pattern, in favour of mediator
[EventDispatcher] tweaked README
minor #9661 Removed observer pattern, in favour of mediator (fabpot)

This PR was merged into the 2.2 branch.

Discussion
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Removed observer pattern, in favour of mediator

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | *
| Fixed tickets | #9344

I don't think this is the best tool to implement the observer pattern.

I just have copied the sentence from:
https://github.com/symfony/symfony-docs/edit/2.3/components/event_dispatcher/introduction.rst

but maybe could be improved with something like:

"Symfony Event Dispatcher is a tool that allows to make your projects truly extensible, facilitating the implementation of Mediator pattern and Publish subscribe pattern"

[edit-1]
I think this could be modified also here:
https://github.com/symfony/symfony-marketing/edit/master/views/en/get_started/components.html.twig

Commits
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ab3e231 [EventDispatcher] tweaked README
b9ad62e removed observer pattern, in favour of mediator
minor optimalization at bundle initialization

fast check to avoid six array method calls
[HttpKernel] made a small optimization to Bundle initialization
minor #9664 [HttpKernel] minor optimalization at bundle initialization (fabpot)

This PR was merged into the 2.2 branch.

Discussion
----------

[HttpKernel] minor optimalization at bundle initialization

fast check to avoid six array method calls

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [|no]
| Tests pass?   | [yes]
| Fixed tickets | #9657
| License       | MIT
| Doc PR        |

That's a rebased version of #9657 on 2.2 + another optimization suggested by @GromNaN

Commits
-------

3330c40 [HttpKernel] made a small optimization to Bundle initialization
4ba6c0b minor optimalization at bundle initialization
updated CHANGELOG for 2.2.11
update CONTRIBUTORS for 2.2.11
updated VERSION for 2.2.11