Stegano

* Stegano now uses OpenCV Python 4.5.4 abd Numpy 1.21.4.

* new: Implemented Shi-Tomashi corner generator
([PR 32](https://github.com/cedricbonhomme/Stegano/pull/32)).
Implemented by thundersparkf (see CONTRIBUTORS.md file).

* Stegano now uses Pillow 8.3.0.

* Stegano is now using poetry;
* minor improvements to the command line.

* fixed markdown of the previous release.

* fixed markdown of the previous release;