Revise option output_function

[schillic]

Internally, we create the option :output_function. It can either be nothing or a matrix, say, A. In the latter case, before we store the reachset X, we apply a box approximation to the set A * X.
I would rename the option (nobody would expect that behavior from the name output_function 😄) and refactor it out of the actual reachability code. This is a typical post-processing task.

[mforets]

Yes, i agree to refactor that code out of the reachability code. We can use a system with output to substitute :output_function and do the post-processing.

[schillic]

I changed my mind here. This is probably the only way to support lazy flowpipes with lazy inputs. So it makes sense to keep it. However, it currently crashes during projection, so this needs to be revised. The option should probably be renamed and become an input option.