Add a timing facility (Refs:#473)

Add a timing facility (Refs:#473)

It is only available in debug mode.

To use: stats_TimerStart( vlc_object_t* , char *name );
stats_TimerStop( vlc_object_t *, char *name );

stats_TimerDump( vlc_object_t* , char *name ) will print a line

TIMER name : last_time - total_time / number of samples (average time)

stats_TimersDumpAll is not implemented yet