Rival to Picatinny riser angled

Found the original didn't quite work with my red dot and Helios - I couldn't get comfortable cheek weld and ran out of adjustment range on the red dot so I remixed this design for my needs. Changes:

- Added 20mm of rise for better eye alignment
- Angled rail down 3 degrees to help compensate for parallax error
- Shortened rail by about 10mm

Prints vertically without supports.