Add a backend for ArrangoDB

[oubiwann]

(Formerly AvacdoDB)

This might be nice for the intrinsic graph-like nature of connected rooms in a MUD ...

• Project page: https://www.arangodb.com/
• Github: https://github.com/arangodb/arangodb
• Docs: https://www.arangodb.com/docs/stable/
• Erlang driver: https://github.com/ErlGameWorld/eArango

[oubiwann]

ArangoDB doesn't currently support Apple M1 ARM. Backlogging ...