feat: let nothrow be a filter

[antongolub]

closes #714

(await $`exit 42`.nothrow(42)).exitCode                               // 42
(await $({ nothrow: [42] })`exit 42`).exitCode                        // 42
(await $({ nothrow(code) { return code === 42 } })`exit 42`).exitCode // 42

[antonmedv]

Do we really want this complication? Not from implementation perspective, but from API perspective.

I think simple boolean flag is much nicer API. And implementing custom filtering logic in catch is trivial.

Unless there is a common use case for such API. I can not see any.

[antongolub]

¯\_(ツ)_/¯

`p.catch` is fine, but try-catch...
try {
  $.sync()
} catch (e) {
 
}

[antonmedv]

let p = $.sync`cmd`.nothrow()
if (p.exitCode == 1) throw err