* Added control/tests/sysnorm_test.py
* Added additional tests and warning messages for systems with poles close to stability boundary
* Added __all__
* Do not track changes in VS Code setup.

* Use of warnings package.
* Use routine statesp.linfnorm when slycot installed.
* New routine internal _h2norm_slycot when slycot is installed.

* type check when calling ct.norm
* metod argument in ct.norm (slycot or scipy) using function _slycot_or_scipy from ct.mateqn

Change in sysnorm_test.py
* set print_warning=False

* In sysnorm_test: Use pytest.warns context manager

* sysnorm_test: Use default tolerance in the tests.