Add $this->nextMockedMethod handler to simplify mock management.

Currently, it's possible to set default value of all arguments of a method to null in a mocked class.
To do that, you should do in a test method:
```php
$this
   ->if(
      $client = new testedClass($socket = uniqid()),
      $this->function->socket_write->doNothing(),
      $this->mockGenerator->orphanize('__construct'), // the trick is here!
      $heartbeat = new \mock\command\request\heartbeat() // So it's possible to create an instance of heartbeat class without any argument!
   )
   ->then
      ->variable($client->sendAcknowledgement($heartbeat))->isIdenticalTo($client)
;
```
I think that it's not simple and not intuitive.
So, this PR introduce an another solution to do that:
```php
$this
   ->if(
      $client = new testedClass($socket = uniqid()),
      $this->function->socket_write->doNothing(),
      $this->nextMockedMethod->__construct->canHaveNoArgument(), // The new syntax is here! 
      $heartbeat = new \mock\command\request\heartbeat() // So it's possible to create an instance of heartbeat class without any argument!
   )
   ->then
      ->variable($client->sendAcknowledgement($heartbeat))->isIdenticalTo($client)
;
```
Moreover, you can do:
```php
$this->nextMockMethod->doesSomething->doesNothing();
// which is equivalent to
// $mockController = new mock\controller();
// $mockController->doesSomething = function() {}; // Or // $mockController->doesSomething->doesNothing()

$this->nextMockMethod->doesSomething->canNotCallItsParent();
// which is equivalent to
// $this->mockGenerator->shunt('doesSomething');
```
Finally, this PR add unit tests about test\mock\generator.