Don't autoHide menu when mouse is released and don't select option when off menu

I didn't see the other pull request about the menu item selected, so sorry for the duplicate there, but I also don't think the menu item should be selected if the mouse is off of the menu item. I fixed this differently than he did though. 

In addition to that issue, I have also added a new `autoHide` option so you don't have to hold right click to keep the menu open.  I move the mouse movement code into a function to be used in both cases (i.e. ctxdrag and mousemove events).  `autoHide=true` is the default (and previous) behavior.  If `autoHide = false`, when you right click, the menu stays there until to left click.