Add basic lww register

Either user provides a timestamp, or we do (but don't recommend
user mixes both operational types)
Correct docs (does not use DVVSet.)
WIP commit of EQC for multi
 Add EQC test for the Map type

Add `init_state/0` to CRDTs that can be stored in Map.

Update Map semantics for remove; drop the value from the value list
concurrent update / add will create a new value on list.

EQC state uses actual CRDTs, should probably use CRDT Mod EQC funs.
The statem model for the Map is exactly that described in Carlos's
draft paper (a triple of {K, V, UUID}), it shows that our
optimisation matches the spec whilst being compact.

Also, the paper doesn't use Types in Keys, so `add` will fail if
the types don't match.