onSubCycle function for "step sequencer" style rhythm notation

[daslyfe]

I meant to put up a PR for this last year after we discussed it, but we could not figure out how to name the function. I thought of a good name today so here is the pr :)
Example: https://strudel.cc/?A3sRLsdfgjhP

[yaxu]

Version from discord discussion:

const beat = register(['beat'], (t, pat) => {
  let div = 16;
  if (Array.isArray(t)) {
    if (t.length > 1) {
      div = t[1];
    }
    t = t[0];
  }
  t = Fraction(t).mod(div);
  div = Fraction(div);
  const b = t.div(div);
  const e = t.add(1).div(div);
  return pat.fmap(x => pure(x)._compress(b,e)).squeezeJoin();
 }
)

[yaxu]

Following more discussion on discord:

const __beat = join => (t, div, pat) => {
  t = Fraction(t).mod(div);
  div = Fraction(div);
  const b = t.div(div);
  const e = t.add(1).div(div);
  return join(pat.fmap(x => pure(x)._compress(b,e)));
}

const {beat, beatOut} = register(['beat', 'beatOut'], __beat(x => x.innerJoin()));
const {beatIn} = register(['beatIn'], __beat(x => x.outerJoin()));
const {beatSqueeze, bsq} = register(['beatSqueeze', 'bsq'], __beat(x => x.squeezeJoin()));

s("bd:4 sd").bsq("0,<1 1 2>,3,5,8,<12 11>","16")

Maybe we can use a proxy object to make beat.squeeze etc possible.