Remove non-ascii characters from codes. Mostly comments are affected.

This is a general cleanup MR.

In this MR the non-acsii charactes are removed from the *.cxx, *.h and *.f files.

The search fro files with non-ascii (almost) characters was performed with:

find       . -type f  -not -path "./.git/*"  -name "*.h"    -exec  grep  -lP '[^\0-\x7f]'   {} \;

• Most of the replaced characters are in comments and originate from a copy-pasted documentation (e.g. from PDF files).
• Some are just math symbols greek letters/umlauts/ characters with grave/acute accents, etc.
• Some charactes are "special empty spaces" or quotes.
• Virtually all the occurances are in the comments. Some exceptions are attempts to cout:: greek letters.

The author names with umlauts/grave/acute accents were left "as is".