calculate the speed
when you walk on the treadmill, you will also walk in the virtual world
add things to do
display how many trials last
update distance settings
add instruction sounds at the start and end of a trial
1.  data will save at "subjectName.txt"
2.  open every files can directly open main.py
ignore .pyc
add three demos: no jitter, horizontal jitter and vertical jitter
now we can measure the baseline level of head-motion in both standing and walking conditions
add some  comments about the data saving for baseline.oy
update things to do
change the order
add nTrialPerJitter
ignore /data
move the mouse away during the expt
init three conditions of baseline_static
ATTENTION: the code is imcomplete
and don't forget to differ the filename where the data saved
baseline_static    have not been tested yet
1. fix bugs in baseline_static
2. fix the resolution problem
add the parameter of Kalman filter