Allow the packager to decide if she wants to compile/install
programs, VAMP plugin and LADSPA plugin.
if --disable-programs is used, then sndfile is not required.
if --disable-vamp is used, then vamp-sdk is not required.
if --disable-lapsda is used, then lapsda is not required.
* Added an initial "formant preservation" option when pitch shifting
* Real-time pitch shifting now uses a faster method by default, with
less variation in CPU usage
* The code is more amenable to compiler auto-vectorization (through
e.g. gcc --ftree-vectorize).
