[2.6] Add documentation for new controller helpers

[dkisselev]

2.6 comes with those new redirect shortcut helpers:

http://symfony.com/blog/new-in-symfony-2-6-new-shortcut-methods-for-controllers

But it doesn't look like the docs have been updated to show them yet:

http://symfony.com/doc/current/book/controller.html#redirecting

[xabbuh]

Hi @dkisselev, you're right that the book currently misses documentation for this feature, but luckily @Cydonia7 already opened a pull request for this: #4109

[dkisselev]

Sweet, thanks, I took a look through the issues and didn't see it but forgot to check PR's.

[xabbuh]

@dkisselev Never mind. :) We can just keep this open until the pull request gets merged in case others do the same search.