DynamicCore doesn't handle named only arguments properly

[pekkaklarck]

For example, arg in this example isn't handled properly:

class Example(DynamicCore):
    def __init__(self):
        super().__init__([])

    @keyword
    def kw(self, *, arg):
        print(arg)

Libdoc reports arg as a normal argument, not as named-only as it should. Luckily execution like

Kw    arg=value

works as expected so named-only arguments aren't totally broken. Invalid usage like

Kw    value

isn't handled properly, though.

[pekkaklarck]

This was initially submitted to Robot's tracker as robotframework/robotframework#4644.

[aaltat]

So do I get it correctly that in the above case, PLC should return ['*', 'named']?

[aaltat]

Add #117 tests