PR #1432 introduced an on-the-fly recalculation of the filter coefficients, whenever the filter parameters change. It turns out this consumes too much CPU for voices that heavily depend on e.g. modulating the IIR filter.

This PR addresses this problem by avoiding direct calls to sin() and cos() and instead using a lookup table for calculating the filter coefficients.

TODO:

• Eliminate the dependency on the sample rate in fluid_iir_filter_init_table()

Fixes #1481