Mixdown functionality.
* Mixdown possible via libsndfile and ffmpeg!
* Fixed some ffmpeg deprecation warnings
* Mixdown UI only shows working Container, Codec and Format combinations!
* Minor bugs and warnings fixed
FFMPEG was reallocating buffers it didn't own and wasn't allowed to. This workaround should work now flawlessly.
Also fixing a bug regarding unpacking sounds, the UI stated unpacking to //audio/filename while it was unpacking to //sounds/filename
Some points of the refactor not sorted by importance:
* Fixed immutability of readers and factories (there are exceptions...)
* Fixed copy constructors and = operators
* Removed messaging system
* Removed reader types
* Added const where possible
* Using initalisers when possible
* Avoided use of pointers when possible
* Removed AUD_NEW and AUD_DELETE macros
* Removed useless NULL pointer checks
* Fixed exception catching
* Fixed some yet unknown bugs
* Lots of other stuff
* Refactored the whole audaspace library to use float as sample format over all readers.
* Added new Readers like the linear resampler, envelope, lowpass, highpass and butterworth.
* Note: The butterworth filter isn't working correctly, some bug in there... Maybe also true for the envelope.
* Added a sound to f-curve operator that behaves mostly like the soundtracker script of technoestupido.
