* task now takes an optional keyword `group`
* added result_group() and fetch_group()
* added group column to Success admin
* group column in searchable
* added `name` field to Schedules
* Scheduled tasks take schedule name as group
* added a synchronous cluster simulation
* added a test for the sync function
* moved signing into its own module
* refactored imports to solve circular import problems stemming from the task module pretending to be a cluster
* added documentation for the new sync option
The core module was becoming too large.
By splitting it in cluster, monitor and tasks it becomes more manageable. It also reflects the documentation structure.