57 face brilliant cut diamond (fixed)

Brilliant cut diamond with 57 faces.
Inspired by thing:50915 by takuya, but rewritten to be more correct. (original script produces incorrect results with diameter != 20)

(FIXME: one of 3 crown angles is not a true parameter - it's just matched by hand, but should be in fact calculated from the other two. It seems if trying to resemble real cutting process, cag4 should be calculated from cag3 and cag5...)