When we finished processing the history it might be possible that we
need to skip some samples from the input. Implement this by adding
a start offset for the samples in the buffer.
start with a completely filled resampler so that the first
input byte immediately gives an output sample. When then have
n_taps/2 leading (almost) 0 samples.
Also make the passthrough resampler act like the real resampler
by introducing an n_taps/2 delay.
Add a sinc based resampler that, unlike speex, avoids memcpy and
works directly on the source data. It also allows for ssse3
optimizations and aligned loads. It will later switch to table
interpolation when doing variable rate.
