Improve cx_freeze compatibility.
Add recursive option to `scriptlib.rm()`.
Add new release tools for Windows version (using cx_freeze).
[Calc] Add an option in UI to solve equations in C.
Improve complex solving, and add tests.

Also intercept errors when sqrtdenest() fails.

TODO: Fix failing tests (systems solved in complex field).
      One problem is that Intervalle() and set() do not have
      the same API. Intervalle() union and intersections are
      done using operators + and *, while set() use | and &
      for the same purpose, so Intervalle() should be made
      consistent with set() API.
Intervalle() support & and | operators (for compatibility with set()).