Updated event_listener.rst

Updated event_listener.rst to use the new KernelEvent::isMasterRequest method
Added Versionadded directive to event_listener.rst

Added missing Versionadded directive to event_listener.rst
Added KernelEvent::isMasterRequest method reference
Fixed internals.rst syntax
document the default value of the form's compound option
add the action option and the method option to the introductionary table, remove doubled include of them
fix the order of the options in the table to match their order below
move versionadded directives for form options directly below the option's headline
[#3752] Adding the question helper to the helper list and marking dialog as deprecated
Fix typo.
add missing 's' for plural.
added a note about types we support
[Form customization] added block_name example.
[Form customization] fixed minor typos
Update standards.rst

Added space line after if statement
Update .gitignore example

As confirmed by WouterJ on Stack Overflow [1], the example
.gitignore file [2] is not up-to-date.

This commit updates the documentation to reflect the current state
of the .gitignore file that is included in the Symfony Standard
Edition distribution [3].

[1] http://stackoverflow.com/q/23437768/1001110
[2] http://symfony.com/doc/current/cookbook/workflow/new_project_git.html#initial-project-setup
[3] https://github.com/symfony/symfony-standard/blob/master/.gitignore
Update the complete 'Initial Project Setup' paragraph

As proposed by WouterJ in https://github.com/symfony/symfony-docs/pull/3827
this commit rewrites the 'Initial Project Setup' paragraph.

The documentation now describes the recommended way of creating a
new Symfony2 project, using Composer to download the Standard Distribution
+ vendors (instead of downloading the zipped version). As the Standard
Edition already contains a .gitignore, the example is replaced by a
link to the one stored at GitHub. The article also explains which files
are excluded by .gitignore.

The last step (downloading vendor libraries using Composer) is removed
as this is now covered by step 1.
[Contributing] consistent headlines
[Components] consistent headlines
fix the wording in versionadded directives