Implements simple boolean flag that converges towards being enabled.

The CvRDT starts with the value "off", and has a single operation, "enable", which changes the value to "on", where it stays forever.
Implements simple boolean flag that converges towards being disabled.

The CvRDT starts with the value "on", and has a single operation, "disable", which changes the value to "of", where it stays forever.
Merge branch 'lenary-bool-crdts' into crdt_lib