Restructure introduction of booleans and boolean logic

[Niolon]

At the moment our section on boolean logic is targetted at people already familiar with formal logic. Rework the explanation. A connected issue is the introduction of booleans without any application e.g. the < > == operators to generate booleans.

It could be investigated whether we want to introduce booleans in the if section. On one hand it would directly connect them with an application. On the other hand, removing it from the beginning would render the generalised operator slide non-functional at the position where it currently is