K8200 extruder improvement

Between filamentdrive and hotend the K8200 has a thermal insulation made of teflon. The filament is heated in a fairly large and undefined area depending on temperature and feeding speed. In addition, the volume of the hole in the teflon cylinder increases with pressure and with temperature. Both factors mean that in slic3r the retrack must be set to a few millimeters. Nevertheless flow of filament does not stop. It's not possible to produce multiple parts in one operation without blobs and thre