Created intro text of the Twig Reference
Added functions section
Added filter section
Created tags section
Added 'almost core' bundles
Fix typo
Created introduction and toctrees
Created DialogHelper documentation
[WIP] FormatterHelper docs
Minor grammar tweak in service container documentation
Correcting method names in config component example
[YAML] minor fix (loader => yml)
Made all namespaces Acme\UserBundle to be consistent throughout document instead of some having Acme\UserBundle and some Acme\Bundle\UserBundle
Changing some uses of we/let's/our
Fixed syntax error.
Added example of non standard 'X-Requested-With' HTTP header.

This example is giving an example on how to add a non standard header,
and as well reminding the user to add a 'HTTP_' prefix, so the custom
header gets sent.
Added missing ',' to example code array.
Updated "Load security users from database"

I've updated the "How to load Security Users from the Database" cookbook to include fix this error:

PHP Fatal error:  Call to a member function getRole() on a non-object in /vendor/symfony/symfony/src/Symfony/Component/Security/Core/Role/RoleHierarchy.php on line 47

which is happening in PHP > 5.4.
The fix is taken by this issue: https://github.com/symfony/symfony/issues/3691#issuecomment-9831914
Updated "Load security users from database"
Using id for serializing, refreshUser with id

Serialize with only the id field, refreshed user is called by id