feat: add headers

[Maschga]

Ref #100

[naltatis]

FYI: It's allowed to have the same query key multiple times. order is guaranteed when parsing:

const params = new URLSearchParams('?foo=a&foo=b&foo=c');
params.getAll('foo');  // ['a', 'b', 'c'] — always in this order

[Maschga]

That would, of course, be a nice way to place the headers as an array in the query string.
The creator of the URL just has to pay attention to the order.
But I think that a note to pay attention to the order is a nice solution.
Thanks for this idea!

[Maschga]

Closing due to lack of feasibility.