Use LMDB_File 0.006 OpenDB
Enable maxreaders attribute
use DB->drop for clear method
No longer need to pass undef to delete
v0.002000

 [Bugfix]
 - use newer LMDB_File to have ->OpenDB work.
 - enable maxreaders attribute.
 - use DB->drop for the clear method.
 - Don't need to pass undef to delete any more.

 [Dependencies::Stats]
 - Dependencies changed since 0.001000, see misc/*.deps* for details
 - runtime: ↑1
post-release cleanup