Open rocksdb in ReadOnly Mode

[cisaacson]

Is there an option that can be passed to level/rocksdb to open rocksdb in ReadOnly Mode? I see how to do it from native code, but not from the level(path, options). I would like to have one process in read/write mode, and another process in ReadOnly mode (even if that means it is only a snapshot of the database at the time of open, that is OK).

[eugeneware]

@cisaacson I've created a PR for this in #98 and also published a personal fork of the leveldown module at @eugeneware/rocksdb