- creating a new entity should be on creation of `?e :db/id ?v`, currently it's when a
  entity id is encoded
- how to retract? 
  do you have to encode in order to retract?
  or i guess try to lookup the values and quit if they don't exist? kind of extra busy
  work ...
- how to update? (amend?)
  something about reference counting encoded values and removing them when they are no
  longer in use ...
