Support for *args and **kwargs arguments

[piccolbo]

we could use special names _args and _kwargs. They could be be initalized with param, meaning that the same properties apply to all arguments in that group. Default or position don't apply but one may want to convert each of the *args to int, or validate each of the kwargs in some way

@autosig(Signature(x, _args, _kwargs_)
def f(*args, **kwargs):

Or one could extend param with an argType selector between regular, var arg and var kwarg.
This way one is limited to these two names, which covers 90% of usage maybe but it's limiting