Pynih doesn't replicate Python behaviour wrt reordering function arguments

[atilaneves]

With pyd, this D code:

void fun(int i, int j, int k=2, int l=3) { }

Is callable in Python with any of:

fun(0, 1)
fun(0, 1, 2)
fun(0, 1, 2, 3)
fun(0, 1, l=4, k=5)
fun(j=1, i=0)

The required parameters are all reorderable as they would be given a similar Python function definition. The pynih backend doesn't currently allow this.