Allow non-WAL mode

[greenrobot]

Wouldn't mind having two versions; e.g. original mdb_get and mdb_get_wal. Would be nice to have a choice. Unless that makes things more complex ofc. Anyway, I'm looking forward very much to your results!

Let's say you have two data "partitions" (e.g. using key prefixes). Partition A is read heavy with few writes, and B is write heavy with few reads. You would only want to enable WAL for B.

Having two separate MDB_envs may not always be an option because of transactions: e.g. modifying partitions A and B in same transaction.