Added BEANSTALK_JOB_NAME pattern functionality to BeanstalkClient.call()

[colevscode]

BeanstalkClient.call() will use settings.BEANSTALK_JOB_NAME pattern to derive the function name if appname and jobname parameters are passed

Makes it easier for folks like me to manage staging and production servers with the same code base. I don't have to write special code to switch the function name given the deployment environment.

Also added some documentation to make the feature a bit clearer.

Note: I tried to select just one commit for this pull request, and to ignore some other changes I've made on my fork. I'm curious if I'm using this github feature correctly. If you decide to pull my changes, please let me know if it works.

[jonasvp]

Sorry for not getting back to you sooner. Looks good to me but I'll have to test it on my development machine. I'll let you know as soon as I tried it out.

[colevscode]

Yeah, looks like this pull request included two commits, I was trying to only submit the last one.