Create Mnemonix.Conn struct

[christhekeele]

Rather than returning the raw t:GenServer.server/0 for consumption in the Mnemonix API, we could instead wrap that value in a Mnemonix.Conn struct.

There are several cool things we could do with a struct instead:

• Implement the Access protocol to support Kernel.put_in and ilk
• Implement the Collectible protocol to co-erce data into a new store via Enum.into/2
  • This gives us a better Mnemonix.new
  • This gives us analogs for:
    • Map.from_struct/1
    • Map.merge/3..4
    • Map.split/2
    • Map.take/2
• Implement the Enumerable protocol to iterate over store contents
  • This gives us analogs for:
    • Map.keys/1
    • Map.values/1
    • Map.to_list/1
  • Stores would have to be able to opt out
• With both of the above, only Map.equal/2 would have no analog
  • Until the inevitable Comperable protocol
• Convert the Mnemonix API into a protocol and implement it for Mnemonix.Conn
  • Could also implement it for Map real parity with in-mem data stores
  • Could grant other structs access to the API in custom ways that don't mandate the GenServer wrapper

Of course, there are some issues:

• It's another layer of indirection
• Need to consider how to create structs for the same store in different processes consistently
• Probably would expand the initialization API beyond just start_link
• The protocol thing is really just kind of silly

Merits some more experimentation.