Ellipse intersection shape

This OpenSCAD script will generate a 2D shape based on two partially overlapping ellipses
The radii of both ellipses are controlled by specifying the final width and height of the created shape as well of the ratio of the depths of each side
there is also an option for rounding the shape while preserving it's dimensions with controllable radius

Author: Mark Gaffney
Version: 1.3
Date: 2013-03-19

Todo:

Warning:
If band_depth > band_width the alignments might not work correctly
If rounding_rad is large compared to band_depth or band_width the shape may just generate as a circle

Changes from previous versions:

v1-3
- added abilty to optionally create 3d lienar/rotate extrusion
v1-2
- Some more control over centre and rounding in preparation for integration into ring creation script
- Fixed some alignment issues
- Made compatible with "Customizer"
v1-1
- uses formula for an arc taken from here http://www.mathopenref.com/arcradius.html

v1-0
- uses