Added F32 version of Teensy Audios state variable filter

[dronus]

A F32 version of Teensy Audio's great state variable filter.

Works well for me. However, there are some things to consider:

• The octaveControl width and resoncance Q factor are unclear by a factor of 0.5 each. It seems to work right now, however I think there may be a difference of factor 0.5 in comparison to the int math done by the Teensy Audio int version.
• As exp2f is too costly, the control signal is only linearly interpolated along each block. Maybe someone knows a better way, maybe adapt some approximation scheme as the int version does.
• A new parameter limit is introduced, as it is not useful to limit against 16bit int limits. Currently this limit is employed in line, so it hard limits on resonancy too. This proved far mor stable for me, but is an deviation to the int version of this filter. Maybe someone could bring some clarity here, and we can remove the in-line limit some day in favor of an output limit, like the int version do.
• There is only one code path for both variable and fixed control.