Rewrite doc using RestructuredText

[egeloen]

This PR fixes #210 and is related to symfony/symfony-docs#6248

[egeloen]

@javiereguiluz let me know what do you think. I have build it with sphinx and all is well.

[javiereguiluz]

@egeloen thanks for updating the format of your documentation. 95% of your doc is right, but there were some syntax issues. These were mostly related to long lines, so instead of adding comments to this pull request, I've created a new one in #214.

The new pull request has been created against the doc branch, so if everything goes right, you could merge my pull request on top of yours and keep working on your pull request until you merge it in the bundle.

Thanks again for transforming all the documentation!

[egeloen]

Thanks as well for your PR! Can you ealoborate about the line length? I have not seen somethink like that in the "Symfony doc" documentation. Is it somethink related to Sphinx or it is only for consistency?

[javiereguiluz]

The line length limit and other specific format rules are defined in this doc: http://symfony.com/doc/current/contributing/documentation/standards.html This limit is not because of Sphinx but because we think this makes the doc more readable in any format and situation (if you read the raw documentation, short lines make it look well).

[egeloen]

Sorry, I was searching the length keyword in the page and not char one... (too lazy to read everything this morning...)

Anyway, thanks for the explanation, let's follow this rule :)

[wouterj]

as these 2 examples are showing different things (config vs widget), I recommend to use 2 seperate code blocks/examples. the tabbed code blocks (configuration block) is often used to show the same feature in different formats.

[egeloen]

Done

[egeloen]

@javiereguiluz I see you remove some code-block tags (for example here). Is it intended for?

[javiereguiluz]

@egeloen yes. This is because Symfony uses a trick to highlight PHP code without creating a very verbose documentation. I don't agree with this trick (I think it's an ugly and dangerous hack) but it's used everywhere in the Symfony docs, so it's "the official way of doing things".

The trick is to remove .. code-block:: php and add two colons :: in the paragraph previous to the code:

BEFORE
If you want to override some parts of the defined config, you can still use the
``config`` option:

.. code-block:: php

    $builder->add('field', 'ckeditor', array(
        'config_name' => 'my_config',


AFTER
If you want to override some parts of the defined config, you can still use the
``config`` option::

    $builder->add('field', 'ckeditor', array(
        'config_name' => 'my_config',