feat: provide format methods for ProcessPromise

[antongolub]

continues #811
relates #764

const p = $`echo 'foo\nbar'`

await p.text()        // foo\n\bar\n
await p.text('hex')   //  666f6f0a0861720a
await p.buffer()      //  Buffer.from('foo\n\bar\n')
await p.lines()       // ['foo', 'bar']
await $`echo '{"foo": "bar"}'`.json() // {foo: 'bar'}

• Tests pass

[antonmedv]

Hmmm, im not sure we need those. Let’s keep API surface smaller?

[antonmedv]

Can we just .text().split ()?