Fix out_codec->frames assignment.
Replace malloc() with calloc() in biquad.c and gain.c.
Add sinc resampler.

I still need to add code to handle draining correctly.
Add worst_case_ratio to effect struct; update code to use it.
resample.c: Don't process data when sample rates match.
Terminate drain loop when frames == -1 instead of 0.

crossfeed_hrtf.c: Replace old drain code with better code.
resample.c: Add correct drain code.

As of this commit, the resample effect should be usable.
Update README.md.