Drawj2d 0.5.1 released

This release adds geometry commands.

Changes:
- new commands ++ (geom.add) and -- (geom.subtract) for vector addition/subtraction
- new commands ** (geom.multiply) and // (geom.divide) for vector scaling
- new commands geom.online, geom.rotate
- mavscript-yacas compatibility improved (escaped unicode chars)