- do funcall isolation on AST
- do self dep isolation on AST
- do if isolation on AST
- implement ForLoop node codegen in Fortran
- add selfdep-in-loop test

https://github.com/inducer/modepy/pull/38#issuecomment-846472970

Doc improvements

Run flake8 in Github CI on target Py version

CI/README: master->main

Shorten, standardize doc/conf

See merge request !48

Furo doc theme

See merge request !47

Run pyupgrade

Placate flake8-quotes