CI: building against php 5.5
Merge pull request #24 from shouze/ci/buildPhp55

CI: building against php 5.5
Move HashGeneration to dedicated Class

In order to use HashGeneration in Notification process, I moved it to a reusable class.

More over, in order to improve quality :
* I replace curl process by Guzzle
* Reduce Public Code API for Client
* Improve tests Client
* cleaning
Add dedicated class to read status from Be2Bill
Rename 3ds callback stuff to generic callback

Behavior will be the same for notification
Be2BillRequest validate hash before creating itself
update tests