* src/audio_output/filters.c, src/audio_output/input.c, include/aout_internal.h,
   modules/audio_filter/resampler/*: Changes that allow the resamplers to set
   the start and end date of the frame it outputs.
   This allows us for instance to output a smaller frame than what we should, and
   keep the rest of the data to compute the resampling of the next frame.
   In short, we can implement much more complex resampling algorithms than before.

* modules/audio_filter/resampler/linear.c: rewrote the linear resampler. The audio
   quality doesn't seem to be better than the ugly resampler, maybe I shouldn't
   have wasted my time on this...