Refactor memory code into separate gem

Love the idea here, I was able to generalize the memory grabbing code into a gem here: https://github.com/schneems/get_process_mem

It would be nice if we could use this code outside of Unicorn-worker-killer as well as reduce the amount of code that must be maintained directly in this library.
Merge pull request #31 from schneems/schneems/get_process_mem

Refactor memory code into separate gem