xpider spartan zero

## a raspberry pi zero based robot

fully customizable via openscad sources.

features:
+ tall dome to accommodate pi zero + motion hat and distance sensor.
+ camera hat supports a standard pi camera and has a socket for different lenses.
+ all gears are tunable thanks to [thing:5505](http://thingiverse.com/thing:5505)

pcbs for pi zero hat:
v1 - https://oshpark.com/shared_projects/jluKwONw
+ initial version

v2 - https://oshpark.com/shared_projects/XhhED3sm
+ add adc mount