BlockBiquad takes kind, f0 (center frequency) & Q (sharpness)
block type arguments and calculates the actual filter coefficients
every frame.

This allows the filter characteristics f0 and Q to be changed dynamically
from LFOs & arithmetic blocks.

A new manual test demonstrates this on a host computer, playing a simple
tone that is dynamically filtered.

…hods

The docstrings incorrectly gave the name of the argument; the code
only accepts the argument name "Q":
```
     { MP_QSTR_Q, MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL } },
```

Synthesizer.lpf takes `Q` as the argument name, use the same convention
here.