Add new graph generators for JMeter-Plugins at Google Code.

Please check new graph generators. You need install JMeter-Plugins at Google Code. 

Please update REAMDE

If you want to use the following methods, you need install 
JMeter-Plugins at Google Code.

http://code.google.com/p/jmeter-plugins.

gc_latencies_over_time
gc_response_codes_per_second
gc_response_times_distribution
gc_response_times_over_time
gc_response_times_percentiles
gc_transactions_per_second