Vamp audio analysis plugin API Code

* Commit updates from David to deal with quantized outputs and
known-range outputs

* Add RDFs

* www.purl.org -> purl.org in generator
* update RDF/XML version of vamp ontology

* we spell quantized with a z in the vamp api

* fix available_plugin (was string instead of uri)

* Restructure output so that each file describes a plugin library rather
than a single plugin (or at least, so that the base uri is for a library --
the file can still contain one or more plugins so long as they all come
from the same library).
* Make it possible to give the library name instead of individual plugin
names on the command line to generate templates for entire library
* Make program accept more than one plugin name, too

* Commit Dan's patch for threshold parameter

* Add identifier to PluginLibrary domain

* Reindent and remove inaccurate comment about usage

* some typo & doc updates -- mostly just because I'm reading it, and fiddling
with a few things as I go along