Added handler code for measuring xen event stats.

[ADD]: Event handler code for "event".
	- Init method to init handler.
	- Handler method to process and store count by
	  domain and port number.
	- Finalize method to print stats collected.
	- Reset method to clear data for lost_records.

[ADD]: Added handler for lost_records.
	- Uses reset method for num_events.

[ADD]: Added Makefile.

[UPDATED]: Updated Trace.h for new event macros.
Added handler for Exception event.

[ADD]: Handler code for Exception event.
	- init, handler, finalize, reset methods.
[UPDATE]: Lost records updated to clear exception data.
[UPDATE]: Updated makefile and main.c for exception event.
Added handler for exceptions_in_xen event.

[ADD]: Handler code for exceptions_in_xen.
	- init, handle, finalize and reset method.
[UPDATE]: Lost recrods for clearng event data.
[UPDATE]: Updated Makefile and main.c
Added handler for interrupt event.

[ADD]: Handler code for interrupt event.
	- init, handle, finalize and reset method.
[UPDATE]: Lost recrods for clearing event data.
[UPDATE]: Updated Makefile and main.c
Fixed code to free memory.

[FIX]: Added code to free malloc'd memory in finalize and reset
	methods.
Added handler for interrupt_in_xen event.

[ADD]: Handler code for interrupt_in_xen event.
	- init, handle, finalize and reset method.
[UPDATE]: Lost recrods for clearing event data.
[UPDATE]: Updated Makefile and main.c
Pretty print stats.
Added handler for hypercall event.

[ADD]: Handler code for hypercall event.
	- init, handle, finalize and reset method.
[UPDATE]: Lost recrods for clearing event data.
[UPDATE]: Updated Makefile and main.c
Refector code to reduce duplication.

[ADD]: Added new generic methods in Common.c that handle events
	and have similar behavior.
[UPDATE]: Update existing event handlers to use the new generic methods.
[UPDATE]: Update Makefile for new and modified code.
Merge branch 'xen_stats'