New Feature, variable extrusion multiplier based on volumetric flow rate

[Leafy1]

This would prevent dimensional changes due to running at a different volumetric flow rate than you calibrated extrusion multiplier at. This effect is most obvious when running variable layer height, the layers printed at lower height, and thus volume flow rate, are always smaller (od smaller, holes larger) than the thicker layers. One ASA-CF part on my desk has a step of 0.3mm on the outside surface between the 0.1mm (11mm^3/sec) and .45mm (25mm#/sec) layers of the print. This effect is due to die swell most likely and would be solved if we could have an optional table with a column for flow rate and one for extrusion multiplier, and have the slicer linearly interpolate between them when calculating the extrusion amount. The calibration print would just print a single wall of nozzle width at max layer height at a handful of different flow rates and you would measure the extruded width with calipers and compare. I have not done enough testing to know if this is primarily related to filament or the nozzle itself, I feel like it should go in the filament settings for most flexibility until more people test it.