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.

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