- Reverts the change to the monolithic `clingo` package in favor of the
previous split between `clasp` and `gringo` since `opam` works with
the latter but not (for some reason) with the former.
- Adds explicit non-support for Python in `gringo`. This is not necessary
for opam.
- Forces usage of the `std::to_string` functions in the C++ standard
library instead of the incomplete alternative implementations inside
of the `gringo` sources.
