Add TimeStatsCollector:
Monitor the time between construct and collect function.
The rendered time a little smaller than the "real" execution time,
because the service is initialized after the Kernel,
but you can still monitor your application evolution.
* Fix notice if monolog is not set
* collectors are not required (if enable_collector is false)
Use $request->server information for more precision
Merge pull request #26 from jdeniau/master

Add TimeStatsCollector + small bugfixes