Named arguments

[ciaranmcnulty]

I didn't check yet whether these work with phpspec - specifically the way we intercept wrapped calls using __call, and whether the array keys are passed through sufficiently

We need to check (and add tests) that this sort of thing works

$this->somefunc(foo: 1);
$this->somefunc()->somefunc(bar: 2);

I imagine similar issues with prophecy, including our wrapping

$double->bar(bar:2)->willReturn(true);
$double->foo(foo:1)->shouldBeCalled();

If it's broken then a short-term fix would be to throw an error early.

[ciaranmcnulty]

We need to check constructors etc. This could just be adding to the feature file added in #1363