* Refactored caed(8) to use virtual inheritance for audio
subsystem drivers.
* Reimplemented the HPI driver in 'cae/driver_hpi.cpp' and
'cae/driver_hpi.h'.
* Added a 'STATIONS.HAVE_MP4_DECODE' field to the database.
* Incremented the database version to 243.
* Added a 'Capability::HaveMp4Decode' value to the
'RDStation::Capability' enumeration in 'lib/rdstation.cpp' and
'lib/rdstation.h'.