o separate Init() from Preamble(), so that we can put the comments
  at the right places.
o Improve and simplify polygon offsetting by not using CGAL but
  Clipper http://sourceforge.net/projects/polyclipping/
o Update license for clipper lib.
o Provide an initial shell parameter.
o Square looks somewhat good and generates smaller files.
o Don't stack offset operations but always go from base polygon.
o Switch to round again - in that case the rounding error and
  path proliferation is not a problem anymore.
o Make base polygon const.
o Update synopsis/readme.