Merge pull request #21 from froj/master

looks reasonable (=
define default proportionality constant for process noise derivation as global constant
add public function to set parameters of process noise covariance
test added public functions (setting process noise parameters)
thou shalt not copy/paste
update visualizer to provide full public interface
Merge pull request #22 from 31415us/master

public interface to allow more fine grained control of process noise covariance
moar constants
Kalman OS integration (sans tests)

Only compiles when you remove the -Werror flag in the Makefile because
of unused variables and functions in kalman.c