added comment to informal robot test file
added support for negative acceleration and fixed bug in robot

bug in robot was that we were doing the kinematic calculations
on the original robot, not the stepped one. It wasn't
causing a problem with any of the tests (even the so far
informal ones) because we weren't checking any changes
except to the kinematic info
changed TICK_DURATION from a constant to a parameter that we pass into robot
changed all values & calculations outside the brain to floating point

(also added stuff to the register functions that pull and push
from the brain to the robot fields, casting to integer when
pulling, and float when pushing)
added 'multiplier' field to all records in register

multiplier is a factor by which to multiply values
being pushed from the robot brain through
a register interface to a robot field, and
likewise by which to divide values being pulled from
a robot field to the robot brain
changed tick-duration so it's a parameter passed into tick-world
removed cut and pasted example text from robot-test
wrote positive acceleration test in robot. but kinematics now broken.