Merge branch '2.0' into 2.1
[reference] Adding the DBAL keep_slave config option
Allow & Force the 'em' option.

Fix to work with Sf2.1 OptionsResolver
Correcting method names in config component example
Changed function definition to match AbstractTypeExtension interface.
Add comma
Merge branch 'remove_min_max_length_references_2.1' of github.com:greg0ire/symfony-docs into greg0ire-remove_min_max_length_references_2.1

Conflicts:
	book/validation.rst
[#1864] Tweaking to remove more deprecated constraints
[#1864] Removing a couple more references to duplicated constraints and marking them as deprecated
[#1868] Backporting details about getting Request Accept data to 2.0
Merge branch '2.0' into 2.1
[YAML] minor fix (loader => yml)
Added clarification on routes ending in optional params
Fixing indentation
Adding double backticks around blog for formatting
[#1873] Making note about optional paramters slightly shorter
Made all namespaces Acme\UserBundle to be consistent throughout document instead of some having Acme\UserBundle and some Acme\Bundle\UserBundle
Added more info about no install artifacts
Changing some uses of we/let's/our
Fixed syntax error.