First stab at my sub

First stab at my sub

This does just enough to get things to compile.

They currently do weird things in edge cases, including ‘Bizarre
copy of CODE’.

‘my sub’ now produces a SUB token, and goes through the same grammar
rule as ‘state sub’ and just plain ‘sub’.  The separate MYSUB branch
of the barestmt rule will go soon, as it is now unused.