Min/Max priority and PID actions, documentation

I'm not sure what the flow for a plugin update is, so I incremented the version from 1.0.0 to 1.1.0 and the build from 4D to 4E.

There are a few caveats here. I'm not sure why there was no get PID action was implemented, but that may be due to unexpected behaviour in applications with multiple processes (e.g. iTunes).

Also, the plugin sort of makes a mess of priority and niceness. As far as I can tell, *both* properties exist for running processes in OSX, but this plugin only affects niceness... even though it tries to use `setpriority`. I tried to stay as closely as I could to the existing terminology.