This replaces all user-defined variable names with continuously numbered
ones so that they don’t lead to syntax problems in ASP, while still
unique and distinguishable. For instance, this avoids problems when
variable names contain hyphens, which are allowed in PDDL identifiers
but not in ASP variables.
Due to a mistake in commit 6d07fcb, the closing parenthesis and period
at the end of initial state facts was omitted. This adds these back in
order to solve this syntax error.