Validate arg nb

Validates the number of arguments, add a few tests for various cases around that.

Gli now uses strict argument validation.
Defaults to no argument validation.
New scaffolded applications are using strict argument validation.
_with_clue_ is still used, but now it also displays stdout, stderr and results (if the test is generating some).
All the reset of these is handled by the setup/teardown, so no need to explicitly pass _results_ to _with_clue_.