Saw, Square and Sample and Hold interpolation

[kdulcet]

While creating a patch, I discovered that the saw interpolates across +10v-0v, which causes problems when using it as an index with something like PdArray. It would be helpful if the Saw, Square and Sample and Hold waveforms had an option to not interpolate when using it as an index.

[baconpaul]

Turns out I did pulse trigger and s&h https://github.com/surge-synthesizer/sst-basic-blocks/blob/4276b8fc23ba36403ff34faf25ab3b42af534f54/include/sst/basic-blocks/modulators/SimpleLFO.h#L249 just not saw