add material on Floyd-Hoare logic

[klaeufer]

https://en.wikipedia.org/wiki/Hoare_logic

Tie to static verification?

Also look at

• https://formal.kastel.kit.edu/~schmitt/
• https://www.key-project.org/
• http://www.envisage-project.eu/proving-android-java-and-python-sorting-algorithm-is-broken-and-how-to-fix-it/