major design reconsiderations see description

added some bike handlebar style tube plugs (printed and tested). more
importantly am changing the vertex style -- old style was too
monolithic. there was warping on the corners and the print took long.
the new design splits each vertex into 3 parts. all motors are
top-mounted (one in each corner), downward facing and interior to the
printer. this makes sense because it provides balance through symmetry
and leaves the box-shaped exterior available for enclosure. also, the
wiring for each motor will be conveniently located near a conduit hole
for clean cable routing. all 4 top vertexes are exactly the same --
which is also nice. remaining challenge is to figure out where the
z-axis linear rods go.. but really they could be placed anywhere.