on computing act_vel and cmd_wheel_speed
build J_2 using diag mat type
odom nav in sim
Merge pull request #29 from tttor/nav-5

Nav 5: odom nav in sim.
Merge pull request #28 from deanzaka/master

add tracking code
fix the structure of tracking code
Merge pull request #30 from tttor/fix-tracking-dir

fix the structure of tracking code
remove bin of tracking
add some tips and refs