Database encryption

A number of current/potential Couchbase Lite developers want to be able to encrypt their databases. (This is a requirement in some areas like healthcare, and strongly desired by financial institutions.) We'd like to have a way to do this with ForestDB.

The desired behavior is that a symmetric key would be provided when opening the database, and all file I/O would be encrypted using that key (transparently, without affecting access via the public API.)