customizable Bridge torture test with Height customisation

this is a modified "bridge torture test" by Triffid_Hunter

the changes are as follows.
a) added a variable to change the leg height, so you can make it shorter to use a bit less filament, or taller if you so choose (i usually use a 5mm height)
b) added notes as to how to remove the top circle from, the top. to do this you need to use open scad, as it uses comments, and not variables.