Manual rebase of the avoid_crossing_perimeters feature
Make the motionplanner work again after recent changes to approximation
Better implementation of the external motion planner
External motion was crossing still too much
Dynamic extrusion width for better gap filling
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	README.markdown
	lib/Slic3r/ExPolygon.pm
	slic3r.pl
Unfinished work for decoupling GUI from the Print object (goal = more speed for manipulation, less memory usage)
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	README.markdown
	lib/Slic3r/Config.pm
	lib/Slic3r/GCode.pm
	lib/Slic3r/Print.pm
	slic3r.pl
Merge branch 'master' into dynamic-flow

Conflicts:
	lib/Slic3r/ExPolygon.pm
Support legacy config files not containing first_layer_height #631
Adjust M-codes for temperature handling for Teacup. #539
Releasing 0.9.2
Bump version number
Fix MANIFEST. #656
Remove the initial retraction compensation. Not only it is not very good for multi-head setups, but it also caused wrong first layer Z when lift was enabled. #655
Consider single walls as external perimeters. #661
Use support material extruder for brim. #653
Fix regression causing SVG/DLP support material to crash the application. #668
More unfinished work
Warn the user when Slic3r is being run under 5.16