Encrypted layer over the dbm library: access to serverless, key-value databases with symmetric encryption.

This library provides an encrypted layer on top of the Dbm and Cryptokit packages. The improvements over Dbm are:

• A single database file may contain several independent subtables, identified by a name (a string).
• Each subtable can be signed and encrypted individually, or encrypted using a common password.
• The whole file can be signed.
• Obfuscating data is -optionally- appended to keys, data, and to the whole table, so that two databases with the same content look significantly different, once encrypted.
• Encryption is symmetric: encryption and decryption both use the same password.
• Signature is symmetric: signing and verifying the signature both use the same signword.