Zttp is really simple Guzzle wrapper designed to provide a really pleasant development experience for most common use cases.
If you need more functionality, just use Guzzle :)
Real documentation is in the works, but for now read the tests.
$response = Zttp::withHeaders(['Fancy' => 'Pants'])->post($url, [
'foo' => 'bar',
'baz' => 'qux',
]);
$response->json();
// => [
// 'whatever' => 'was returned',
// ];