Refactoring

Based on https://github.com/salimane/php-resque-jobs-per-fork
Modifications: 

* Parent pre-forks child. Child reserves jobs. (only tested with 1 worker per process)
* Signal handling improved
* Child terminates when parent dies unexpectedly
* Parent propagates signals to child (pause, continue, quit)

Isn't a doneWorking call necessary here?