Support Maps, not just Entities.

[aadrian]

Support Maps, not just Entities. At the moment this does not seem to really work because:

• there's no way to associate a name for an entity "instance" (or same way to pass a name)
• passing a Map.class as an entity will try to work with a table called map (so no more than one Map can be used in a project)
  • the convention from #55 seems to be missing