hit threshold and hit event added to the primitive collision detection

git-svn-id: svn://svn.code.sf.net/p/vpinball/code/trunk@903 14438d79-0ffd-4333-8ae7-ea2bdd901387
unused primitive events removed and command reference updated

git-svn-id: svn://svn.code.sf.net/p/vpinball/code/trunk@904 14438d79-0ffd-4333-8ae7-ea2bdd901387