parametric tool rack for keyhole shelving

http://www.sodnpoo.com/posts.xml/parametric_tool_rack_for_keyhole_shelving.xml

Based on Timmytool's scad file (http://www.thingiverse.com/thing:15515); configuring the keyhole dimensions is the same:

key_big - diameter of the large round part of the key hole
key_small - diameter of the small offshoot from the main key cylinder
key_spacing - distance from one key hole to the same point in the next key hole
key_thickness - thickness of the material the key holes are cut from

Additionally, to configure the shelf and holes:

shelf_width - width of the 'shelf', centred around the keyhole
shelf_hole_radius - radius of the holes
num_holes - the number of holes

The script will attempt to calculate the depth of the shelf and an even spacing between the holes.