Adds initial topics for build systems and fixes UDL overview

Adds initial topics for:

Passing by value
Passing by reference

Adds drafts for error handling

* exception handling
* categories of errors
* error codes

Adds drafts for definitions/declarations

Adapt folder layout and finish pandoc integration (#69)

Completes the necessary folder layout rework and refactors pandoc file generation to work together with the rest of the tooling/setup. This finally finishes the pandoc integration to automatically generate teaching docs.

Fix extra sources in makefile

Remove currently empty sections from the document

Remove NOTE

remove notes from official released document

Add CI action to run python unittests