doxygen warnings

This is a work in progress and should be merged as soon as possible.

We know, that it's not the best documentation yet, but at least everything has been documented and carefully read.

Follow the boy-scouts rule to improve whenever you pass by at a wrong or incomplete doc string.

Starting from now, we use the "@brief" style (over \brief). and also tripple slash notation.

AS DISCUSSED LAST FRIDAY, THIS WILL BE MERGED ON 22nd OF SEPT.

Closes #63 (closed)