Report Cache Invalidation Locations With DTrace Probe

Fixes #3 

* Move cache invalidation counts to role
* Add ability to check current process privileges
* Introduce cache invalidation locations role
  * Spawns child process to dtrace parent process
  * Uses method-cache-clear dtrace probe
  * Reports dtrace results
* Add example method-cache-clear.d dtrace probe for use outside Busted
* Update README