Insignificant pedantic change to gemspec
Update Gemfile.lock with new version
Add Bumbleworks.start_worker! and rename 'start!'

Instead of autostarting a worker when Bumbleworks "starts" (now a
misnomer, so we should probably rename Bumbleworks.start! to something
like Bumbleworks.init!), this new method supports our recommended best
practice of running workers in separate threads, and using multiple.
Good candidate in a rake task - we'll create one in Railties, at least,
and maybe create a method you can call to create your own (a la Rspec).