Initial implementation of the "infill link maximum distance" feature.
Parts of the perimeter connecting two infill lines will be dropped,
if longer than a given threshold.
Removed the deprecated VibrationLimit feature.
Added triangle infill.
The Prusa3D fork of Slic3r has been marked as "Slic3r Prusa Edition"
with menus pointing to the prusa3d/slic3r github release page
and Prusa3D drivers downloads page.
Made sure the C++ fillers are instantiated at the worker threads,
where there are being released.
Extended the FillRectilinear2 to calculate the contour / line intersection
with exact arithmetics, improved robustness and added error handling
and error reporting, if the contours to be filled are not correct.
