New directions in LMDB

[chjj]

This is a full rewrite on top of the current leveldown codebase.

It passes all current leveldown tests aside from a few I've removed: some LevelDB-specific ones (i.e. compression). The tests that are really failing are the null key/value tests -- I've turned null values into single null bytes ({0}) instead of empty buffers (LMDB doesn't allow for empty values). So, all in all 5 tests are failing, but for technical edge-case reasons.

New additions/changes:

• All modern iterator options are now available.
• iterator.seek() has been implemented.
• All lmdb info/stat properties are exposed via getProperty.
• Approximate size is currently hacked in but doesn't accurately measure disk usage.
• leveldown.destroy() has been implemented.
• sync option has been implemented for put/del/batch.
• notls has been fixed.

New features:

• Online Backups - LevelDB doesn't allow for hot backups but LMDB does. I've exposed it as db.backup(path, callback);.
• noSubdir option.

Todo:

• Upgrade LMDB itself.
• Implement leveldown.destroy().
• Test in practice.
• s/leveldown/nlmdb/g

Hopefully, now we that we have the code in sync with the latest leveldown code, we can maintain this module more easily. I plan on using this module in production eventually, so I'll definitely be around to care about it.

cc @rvagg

[chjj]

@rvagg, any thoughts?

[rvagg]

only thought is that I'm glad someone else has time for this! added you as collaborator and npm owner,

[chjj]

@rvagg, cool. I'll get something in npm soon.