added roessler example, fixed z-ruler problem, 1-2 px points are drawn faster now in Curve::draw()
scheint zu klappen
added mark and circle

this includes the range function for GLWindow instances,
a change in application.cpp to force at least one idle event each loop
an additional __stable__ member of objects which is entered in objects.py/success
and the commands mark and circle themselves in commands.py

also there were minor changes in roessler.dat and lorenz.dat to fit better
with the original exercise sheets