Update to support celery 3.1.7

Since celery 3.1.7 the result queue is durable by default.
Added config variable: TASK_RESULT_DURABLE that defaults to true
Merge remote-tracking branch 'upstream/master'
Updated with information for use with celery prior to version 3.1.7
Fixed some indentations.
Updated important example
Merge pull request #12 from Phantazm/master

Update to support celery 3.1.7+