support for frules with keyword arguments

[oxinabox]

I wrote an frule with keyword arguments
It doesn't look like diffractor is picking it up.

[oxinabox]

Workaround:

Instead of writing
frule((df, dx), ::typeof(f), x; kws...)
I had to write
frule((_, dkw, df, dx), ::typeof(Core.kwcall), kw, ::typeof(f), x)