Add TestCall::content() which returns marshalled payload

[thekid]

Example:

$fixture= new TestEndpoint([
  'POST /users' => function($call) {
    $payload= $call->content();         // (string) {"name":"Test"}
    $data= json_decode($payload, true); // (array<string, string>) ["name" => "Test"]
    return $call->respond(201, 'Created', ['Location' => '/users/'.md5($data['name'])]);
  }
]);
$fixture->resource('/users')->post(['name' => 'Test']);

[thekid]

Hrm, maybe have content() which also returns the formatted content instead?

[thekid]

Reelased in https://github.com/xp-forge/rest-client/releases/tag/v5.7.0