1) New algorithm for connecting along the perimeters is now applied
to Honeycomb, Hilbert and similar planar filling curves.
2) The old expensive path chaining is not applied if the new algorithm
to connect along the perimeter lines is called afterwards.
by @supermerill and @wavexx
WIP: The function Fill::connect_infill() is being rewritten
to utilize spatial structures wherever possible for lower CPU load
and less dynamic memory allocation.
for islands with another islands in their holes.
Improvement of chaining of infill lines for 3D honeycomb, Gyroid and
Honeycomb infill: New TSP chaining algorithm is used.
