Since the database format of LMDB may change from version to
version, it may become necessary to migrate a database when upgrading.
Two predicates are provided for this purpose: lmdb_export/2 and lmdb_import/2.
To ease migration from the legacy library(bdb) library, files exported with
bdb:db_export/[2,3] can be imported into the LMDB format using lmdb_import/2.