resampler: Add a missing break in choose_work_format
resampler: Fix spelling mistakes (fall trough -> through)
resampler: Add comments to choose_work_format.
resampler: Add a function for comparing sample format precision
resampler: Use only the sample format in fix_method()

We only care about the format here, not the whole sample spec so pass
the format as an argument.
resampler: Add asserts to fix_method() and choose_work_format()
Resampler: Don't use the peaks resampler for upsampling.

This patch fixes this assertion:
    Assertion 'r->i_ss.rate >= r->o_ss.rate' failed at ../../src/pulsecore/resampler.c:1744, function peaks_init(). Aborting.