Replace kerncase with syntax-parse.
Made tabs into spaces.
Make toplevel checks use internal syntax class.
Remove duplication.
Make tc-expr unit use the new syntax classes.
Convert tc-let unit to new syntax classes.
Switch tc-structs over to syntax classes.
Make syntax classes use literal sets.
Move code around so that auto nested attributes works.
Move syntax class code into internal forms.
Move internal into internal-forms.
Change name of failed-typecheck.