Formeln und Sätze updated

Gunnar Krug found a trivial error in my collection of theorems and formulas for the mathematical olympiad (see math documents). Updated the document, also improving the overall appearance a little bit. However, there’s still so many things I would do different if I wrote the document now (it’s been way back in 2004 or so). But sorry, haven’t got enough time to fix these things right now!