Convert to using multi subs on pod2markdown
Convert to using multi subs on pod2markdown

I think this still looks nicer, is more easily extensible, and it seems to work
a little better. Just by making this change I eliminated a "Cannot invoke null
object" errors, but I do not think any logic changed.

jpve/perl6-pod-to-markdown,zostay/perl6-pod-to-markdown,jpve/perl6-pod-to-markdown,softmoth/perl6-pod-to-markdown,zostay/perl6-pod-to-markdown,softmoth/perl6-pod-to-markdown