adding currency.rst file
Merge pull request #280 from StefTweet/2.3

Update Compenents / dependency_Injection
updating reference/forms/types
Merge remote-tracking branch 'origine/2.3' into origin/2.3
updating finished files of book
fixing typo
updating http_foundation to 2.3
Merge pull request #283 from gregquat/origin/2.3

Updating reference/form/types/* from symfony-docs/2.3