update LMDB to latest stable release version 0.9.23

[mykmelez]

This'll also require publishing lmdb-rkv-sys for the first time (until now we've been relying on lmdb-sys from the upstream lmdb-rs project).

[mykmelez]

@ncloudioj I'm not making any code changes here, just revving the version of LMDB. But it'd still be worth a sanity-check from you that this is a reasonable approach to keeping up with upstream changes to LMDB. (I originally expected to periodically merge changes from the upstream lmdb-rs project, but it doesn't seem to be active anymore, so I think we're going to need to maintain our own copy of LMDB.)

[ncloudioj]

LGTM!

I think LMDB is heading towards the 1.0 release, so its development seems to be slowing down a bit lately.

[mykmelez]

I think LMDB is heading towards the 1.0 release, so its development seems to be slowing down a bit lately.

Woot! I #23 I suggest maintaining a branch of lmdb-rs that tracks the master branch of LMDB, which is where version 1.0 is being developed. Might be interesting, although it isn't a priority for me at this point.

[ncloudioj]

Don't be over-optimistic!!! I've been waiting for the 1.0 release since 0.9.7 (released 4 maybe 5 years ago), they go crazy about the software quality. Hopefully my beard isn't grey when 1.0 hits the road :)