Check root-level constants for framework root

Don't confuse constants defined within our namespace (such as for the
Bumbleworks::Rails engine) with the constant defined on Object.
Add magic entity-specific tags for broadcast/wait

Use of the entity-specific tag feature (with :for_entity => true on the
expression) dramatically improves efficiency, especially with a high
number of trackers waiting for the same tag, but only where entities
match.  Note that this doesn't completely replace the functionality of
the :where => :entities_match clause, since the latter allows for
global tags that can trigger both a global listener and an entity-
specific listener.
Add Bumbleworks::User module

Include this module in a class that represents your users, and you'll
get methods for loading tasks, looking up roles, and claiming and
releasing tasks.