show version with -h option

Hi, 

I found it would be useful to tell which version it is from command line so I add this.

[vagrant@centos58 ~]$ f5_monitor -h
New Relic F5 Plugin version 1.0.7
Usage:
  f5_monitor  ( run | install ) [options]
    -v, --verbose                    Run verbosely
    -l, --license LICENSE_KEY        Your NewRelic account License Key
    -c, --config FILE                Override the location of the newrelic_plugin.yml
    -h, --help