Parameterized Coin Calibration Test

I liked MrJohn's Nickel Calibration Test (http://www.thingiverse.com/thing:11215) but I wanted to use a larger coin, like a Golden Dollar. Also, it's a very simple thing so I figured a an OpenSCAD version was in order.

It's parameterized with adjustable amount of outer margin and slop around the coin.

I've also created a STL file for a dollar coin.