#507 renamed files

[Chris Crawford]

some of the links are broken on
https://docutils.sourceforge.io/rst.html
because .txt files were renamed to .rst:
https://docutils.sourceforge.io/docs/user/rst/quickstart.txt
https://docutils.sourceforge.io/docs/user/rst/cheatsheet.txt
there may be others

[Günter Milde]

Thank you for the report.
This will be fixed soon. (After sourceforge lets me commit from git-svn again...)

[Günter Milde]

Fixed. Thanks again.