perf scripts python: Add a python library EventClass.py

This library defines several class types for perf events which could
help to better analyze the event samples. Currently there are just a few
classes, PerfEvent is the base class for all perf events,  PebsEvent is
a HW base Intel x86 PEBS event, and user could add more SW/HW event
classes based on requriements.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1344419875-21665-5-git-send-email-feng.tang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>