low: proposal stop in wrap (wrap.filter)

[Slava Bereza]

const v = value(1);
const m = v.wrap.filter(v => v);

m(0);
assert(v === 1);
m(2);
assert(v === 2);
m(0);
assert(v === 2);

[Slava Bereza]

Implemented in 0.6.0

const v = value(1);
const m = v.pre.filter();

m(0);
assert(v === 1);
m(2);
assert(v === 2);
m(0);
assert(v === 2);
``