Fix demos

These demos illustrate the use of fixed-point primitives in the SDF domain. These primitives are used to model hardware implementations with finite precision.

Illustration of the different masking options available.
Effect of filter tap precision on the frequency response.
Comparison of a fourth-order direct-form IIR filter implemented with floating-point arithmetic and a similar filter implemented with fixed-point arithmetic.
Testing of fixed-point multiplication over a range of numbers by comparison against floating-point multiplication. The results should be the same.