Wider leather splitter

The leather splitter by parva_donum left usable blade overhanging. I remixed their models to use more blade length and also modeled a blade cap to help reduce deflection.

Take the spacer sizes with a grain of salt; they were developed by trial and error. Actual resulting thickness seems to depend on a bunch of factors like blade sharpness and leather type/temper.

The circular space in the blade holder should accept a small neodymium magnet to hold the blade in place when the cap is loose.