slic3er 1.2.9 stable is out

Autospeed
This is an experimental feature that, as often happened in the past, Slic3r is introducing in the 3D printing world. The purpose of this feature is to keep volumetric speed constant (thus, nozzle pressure too) throughout the print. The sudden pressure changes during the print, which are caused by print speed changes and by different extrusion widths (we like to use thin widths for external perimeters but fat infill, for example) often cause visible quality drop because there's a delay. This problem is very visible in printers having a Bowden extruder or when using soft filaments. Several strategies were tried in the past, including the advance algorithm in several firmware projects, and even a Pressure Regulation feature in Slic3r itself. But this new autospeed feature uses a different approach: it chooses the head speed automatically in order to keep volumetric speed constant. This will cause no pressure change inside the extruder, thus no delay.