[Cookbook][Templating] New way of creating extensions for twig

[ricardclau]

Q	A
Doc fix?	yes
New docs?	no
Applies to	2.1+
Fixed tickets	#2421

Added a note refering to old doc and cookbook for previous versions of Twig and tweaked code to add the Twig filter

[wouterj]

You forgot some linebreaking on the 72th character

[wouterj]

While it's not your fault, can you please update some other fixes to this document for me?

• line 41 - there should be no spaces around the . operator

• some text is not linebreaked around the 72th character (line 118, 18 and 54)

• I prefer to have the PHP example at line 86 like this:

  $container
  ->register('acme.twig.acme_extension', 'Acme\DemoBundle\Twig\AcmeExtension');
  ->->addTag('twig.extension')

[ricardclau]

Changed (I hope) all your comments!

[wouterj]

👍 thank you!

[weaverryan]

Awesome job Ricard - thanks!