Sidekiq support

This may or may not be the most efficient implementation; I simply
repurposed the Resque code and made modifications where required.
Should work without sidekiq gem now.
Oops
Correction to README.rdoc
include Sidekiq::Worker moved to SidekiqWriter
Merge pull request #37 from johnmichaelbradley/master

Should work without the sidekiq gem now.