Allow job classes to define default job options

[myronmarston]

It's nice to be able to set job options directly in the job class; that way, when your app enqueues that type of job from multiple places, each place does not have to pass the same job options to queue.put. Here's an API @dlecocq and I discussed:

class MyJob
  def self.perform(job)
  end

  def self.default_job_options(data)
    { jid: jid_for(data) }
  end
end

Essentially, a job class can define a default_job_options method. If it's defined, queue.put(MyJob...) will use it to get default job options. A single use of queue.put(MyJob...) can override default options by passing its own options.