[TASK] Documentation

** WIP: please don't merge **

This task is all about documentation. The goal is to add extensive documentation to ``vhs``. 

### Changes / Structure

This will be done by:

* modifying all class files, shortening the class doc and arguments doc
* adding doc files for class doc and arguments doc

The documentation inside the class files is only important to source readers and XSD generation. So the goal is to keep it short. The full documentation is available on fedext.net and will be autogenerated from the created doc files. Every class will have its corresponding documentation directory (``vhs/Documentation/Classes/...``). Inside that the ``README.md`` is the class doc and every argument will have its own file inside the ``Arguments`` subfolder called ``<name of argument>.md``. This can (but not must) be used for a long description of the argument. The current doc arg of ``registerArgument`` is called the short description, and must be set.

### Tone

I would like to keep it light and a bit funny, addressing the coder directly with *you*, and provide easy but exhaustive examples (cats, just because).