Make raising signal exceptions a configurable option

Idea credit goes to @nevinera
Add ability to run all available jobs and exit
Use exit_on_complete instead of exit_on_empty_queue

This is just a little more descriptive of what actually happens under the hood.
Add new commands to the README
Move reporting and control code outside the loop callback block

This triggers a LocalJumpError in jruby
Merge branch 'exit-when-done'

Conflicts:
	README.md
Merge branch 'signal-handling'
Prepare 3.0.5 release