Fix copyright years in doc/users/doxygen.html

The year 2013 is already included in the range 2012 - 2014.
Merge pull request #352 from Rombur/fix_step_52

Add instantations for class RungeKutta.
Merge pull request #350 from felgru/doxygen

Fix copyright years in doc/users/doxygen.html
Merge remote-tracking branch 'upstream/master' into add_clear_current_row