added the beginning of a test harness.
Split arm_connect_io.

I splitted the arm_connect_io function into several because it was
against the principle of single responsibility.
Added a test for the cvra dc motor driver.
First tests of real debra code.
First bug found by TDD.

Such bug
How quickly found
wow
working on unit testing properly.
factored out elbow position calculation.
added a function to compute shoulder angle.
Added a function to compute elbow angle.