Improved the Vertical takeoff and landing aircraft notebook (#390)
Improved the Vertical takeoff and landing aircraft notebook (#390)

* Fixed typo in PVTOL notebook (forgot to divide by m). Also replaced hardcoded image with latex code.

* Removed a lot of the unnecessary decoupling code.  Notebook used to say "Since the python-control package only supports SISO systems, in order to compute the closed loop dynamics, we must extract the dynamics for the lateral and altitude dynamics as individual systems." This is not true anymore. So I simplified the code.  Also added explanations as to what the code is doing and fixed some typos.
murrayrm/python-control,roryyorke/python-control,python-control/python-control