A 2.2.52.1 is now available, it fixes some bugs (and a big one that can make some islands disappear).

new & changes

• A way to generate geometry quickly via a script, need to have FreeCAD 0.19 installed. more information
• thin walls: merge path into external perimeter loop when possible. So it will do less travels and less retractions. Also a better quality thin walls when they touch the perimeters. (see picture below taken on my printer with 0.6 nozzle and meter-long bowden that ooze like a boss)
  
• #4 perimeter overlaps : total control over perimeter width vs spacing. These settings may allow you to retain the same perimeter quality when you under-extrude but without under-extruding. Also may help to hide infill pattern passing through the perimeter. These needs some experimentation to see if they are useful.
  • external_perimeter_overlap to control half of the overlap between the external perimeter and the inner one: 0% is no overlap, 100% is full overlap (current & default value)
  • add perimeter_overlap, same between every perimeter (and the other half with the external one)
  • add perimeter_bonding, that shrink the external-internal spacing, without growing the infill polygons.
• little rework of XY compensation, splitting into outer and inner (like holes but without convex detection)
• now using first_layer_size_compensation so i didn't pick up the 'elephant foot' from prusa that is with a reversed sign, but it should convert automagically if detected.
• Layer time preview from @rongith
• layer chronology preview, to see when a layer will be printed.
• #248 #312 add min width for 'only one perimeter' (with decent default)
• #239 add z_step (inverse of slic3r z_steps_per_mm), so every layer is now exactly at a multiple of this value, even if you set it with the manual / variable height tool.
• #211 % max speed reduction for filament cooling
• add external_perimeter_fan_speed setting, from a previous implementation by Justin Schuh

bugfixes in 2.2.52.1

• #327 #317 fix xy hole compensation (can delete 'inner' geometry if hole compensation is set), also some inconsistency fix with multiple regions.
• #333 better python path completion for all os.
• fix bad text for switching to rectilinear if 100%
• #306 fix auto-speed: do not takes into account extremely thin extrusions from gapfill / thinwalls.

bugfixes

• #302 can remove "extra peri on odd layers" even with 0 peri
• only_one_perimeter_top: fix when only 2 perimeters, it can go through the second one.
• use first_layer_size_compensation for the lslices, so the brims are printed against the real lines.
• #183 min z-spacing for support interface layers is 0
• #147 remember the color choice if reslice. But on first colorprint, it switch, then never again. Also on the first multi-extruder print. Also on every extruder count change.
• #306 remove gapfil from autospeed, as it will reduce the speed because of very tiny extrusions

Downloads in the "assets" section below

note: I haven't tested the linux & macos build, as the compiled libraries have changed a bit, they may not work as intended.