Support 56kHz to 19.2kHz gain analysis (Patch v4)

Support 56kHz to 19.2kHz gain analysis (Patch v4)

This implementation uses decimation to generate an estimate of the
required ReplayGain adjustment for tracks sampled at high rates.

This approach avoids having to generate filters with commensurately more taps,
and also the subsequent effect on performance as these additional
taps are evaluated for high sample rate tracks.

Filter table entries with coefficients that are unchanged are
marked /* ORIGINAL */.

The remaining entries are new and have coefficient values obtained
from src/utils/loudness/loudness.sci. See:

        http://lists.xiph.org/pipermail/flac-dev/2012-February/003220.html

Because these filter coefficients can be generated from a known source,
they are preferred to the FooBar2000 coefficients whose provenance is
unknown.

Signed-off-by: Earl Chew <earl_chew@yahoo.com>