Added restart signal support

This can be used when running with unicorn.

rerun -r HUP -- unicorn -c unicorn.rb

NOTE: Make sure you run unicorn with a config file
      otherwise it will respawn the master and end
      up in a very bad place.
Fix Null pointer on $spec
Lock listen gem to 0.7.3
Merge branch 'pr/31'

Conflicts:
	rerun.gemspec

Added changes to the readme.
Updated listen gem