low: proposal join or attach

[Slava Bereza]

const a = value(0);
const b = value(2);
const c = value(2);

a.join(b,c).watch(([a,b,c]) => {});

// or

a.attach(b,c).watch(([a,b,c]) => {});

[Slava Bereza]

Declined after implementation:
02fba76