Lmdb

I'm not suggesting you pull this branch as-is, just wanted to let you know it's here so you can read through it and get a feel for the differences.

Also, we could handle the client/slot/ack lists a bit more cleanly. Since LMDB supports multiple namespaces, we could just have a separate table for each of these instead of kludging the ID# onto the end of the key as the original code does. But this is a direct translation of the functionality, again just to give you an idea.