This would deserve a further look into it, but for now it's impeding development
without providing any meaningful security.

This was a pending TODO: now the Catala program compiled into OCaml should
return better messages and a little more information about uncaught exceptions.

Note that this also concerns, at the moment, compiled modules called from the
Catala interpreter: in this case, it's already better than nothing, but what we
need is proper interoperation between the runtime exceptions and the interpreter
handling (`EmptyError` should already be handled properly since it is critical
to the computation flow, but "error" exceptions are left uncaught and will kill
the interpreter).

This may be part of a bigger task on unifying the output of the runtime and
toplevel, which also concerns computation traces.

Note 2: All runtime exceptions don't have a position available, which is quite
unfortunate when your program hits an error. With `OCAMLRUNPARAM=b` and if
compiled with `-g` (which should normally be the case), you can get an OCaml
backtrace but that's not very friendly. Ideas for improvement:
- The runtime could force-enable backtrace recording (`Printexc.record_backtrace
  true`) to supersede the need for `OCAMLRUNPARAM`. We can also record our own
  handler to print the file position and/or backtrace in the way we see fit
- The printer of OCaml code in Catala could insert line directives so that the
  positions in the backtrace actually trace automatically back to the Catala
  code
- If we don't want to leverage any OCaml machinery in this way, the compiler
  should add position information to any operator that might fail (e.g.
  divisions, date comparisons, etc.).
Note that running in trace mode might already help pinpoint the location of the
error ?

Module names must be capitalised (start with a capital letter), and the name of
the file on disk must match ; however, matching up to capitalisation is allowed,
i.e. the file on disk can start with a lowercase letter.

A mismatch between Clerk assuming generated module artifacts would match the
capitalised module name, and `catala depends` matching the names of files on
disk (because it would otherwise mean treating dependencies differently
depending on if they originate from modules or not) was causing "file not found"
errors later on in the compilation chain.

This patch enforces that the capitalisation of the original file name on
disk (which is always known) takes precedence in Clerk, matching the behaviour
of `catala depends` and fixing the issue. It's also actually a small
simplification in Clerk code.