normal: rename filter to wrap.filter

[betula]

const a = value(0);
const new_a_with_wrap_filter = a.wrap.filter(v => v);

// or maybe
const new_a_as_filtered_source = a.flow.filter(v => v);

[betula]

Add possibility for use flow with another reactive value

const src = value(0);
const dst = value(0);

src.flow(dst);

https://github.com/betula/realar/issues/41#issuecomment-808653992

[betula]

https://github.com/betula/realar/commit/ef48d053602519150718712f0aa6cc20b8e47fb3#diff-a2a171449d862fe29692ce031981047d7ab755ae7f84c707aef80701b3ea0c80L303-R320