Fixed Error in sim_fiction_compensation.m

[jasonnicholson]

sim_fiction_compensation. The main issue is that z was used in the controller and not z_tilde. This bug fix makes the friction observer better. However, a well-tuned PI and velocity gain without friction observer is better than the friction observer; its also easier to tune.

There other updates such as:

• demo1 and generate_ramp_signal.m was redundant so it was delete.
• demo2 - Some of the code was vectorized. Pointed out where forward euler was done because ti can be tricky to get right. Preallocated before for loops when needed.
• demo3.m and sim_fiction_compensation. Extract controller gains from ODE functions so they can be passed in. Fixed error in controller where z was used instead of z_tilde; z is not observable and should not be used in the controller. Shortened the sim time so that more structure is shown. Rise time is shorter. Settling time is shorter. I see indiciations that there still be another error because around 6 seconds, there is a blip in the response. More investigation would be needed.
• fig8 was updated with the new results from demo3.m
• lugref.m was vectorized and the note about Forward euler was added.
• lugref_ss.m was vectorized.
• sim_pid.m - t was unused so made that more clear in the function declaration in line 1.
• sim_stick_slip.m was vectorized.
• demo4.m shows an optimally tuned PI and velocity gain with no friction observer. Performance is superior to friction observer. fig9.png was added.
• README.md was updated to reflect corrected results of demo3.m. demo4.m results added.

TODO:
Optimally tune the PI, velocity gain, and observer gain to see performance can be improved for friction observer results.