Vamp audio analysis plugin API Code

* Add silence detector. But I'm not happy with its results: take a look at
the aubio silence detection code and see what's up

* correct vamp-hostsdk soname

* update .la files

...

* Fix failure to default correctly if plugin output unspecified

* don't allow block/step sizes to be undefined

* Add sdkstatic target

* use correct (?) sonames for libraries (oops)

* avoid trying to use timeval if building on Windows

...