Implementation
  
  Sqlite virtual tables
  
  * Allow a custom backend to be used for data storage and retrieval.
  * C API
  * Wrapped in Perl by Salvador Fandiño's SQLite::VirtualTable
  * To create virtual tables in Perl, just create a class derived
    from SQLite::VirtualTable
  * (e.g. SQLite::VirtualTable::CSV for comma separated values)