Customizable OpenSCAD Chess Pieces

# OpenSCAD Chess Pieces Remix

This is an open source chess set, made with OpenSCAD. It is based on the work of Harpo (https://github.com/quaternionmedia/scad-chess).
I did the following changes:
- I rotated the crown of the queen to get rid of rfix parameter. The new model of the crown is called queen.crown3.stl.
- I unified the rotational alignment of the chess pieces.
- I added a new knight stl file knight4.stl, which differs from the original one knight3.stl in the following ways:
- The original base area was irregularly shaped and not correctly centered. The new model now has a perfect circular base with center at x=y=0.
- The original horse head design required support structures for printing. I bent the horse's head down and made some other minor adjustments so that it can be printed without support structures.
- The comparison image shows the new knight (top row) in comparison to the old knight (bottom row).
- The pawn_profile.svg made problems with certain slicers due to i