Also include support for "sorry" messages so that we have a place
to hang unsupported but properly parsed constructs.
In the process of doing this, I also encountered and add parser support
for indexed names. And matching "sorry" messages.
Add enough rules to parse a simple VHDL program:
Parse library and use clauses,
Parse entity declarations, and
Parse architecture bodies.
Add some parser infrastructure:
Handle syntax errors with useful error messages,
Include file name and line numbers in parse errors,
Add some parser debug aids.
Stephen Williams