Use overlap-save algorithm for conv?

[galenlynch]

We already use overlap-save for fir filtering, when it is advantageous to do so. It seems like it would make sense to also use overlap-save for conv. As fir filtering is just convolution, it's a little weird that we have two totally separate code paths to do the same thing.

[ssfrr]

big :+1: for unifying conv and filt. It's debatable whether we even need separate names for them, but I think that it's nice to be able to easily switch between FIR and IIR filters with filt, and it would be weird not to have convolution and only rely on filt, so I think it's fine to have both.