JMC: Added a simple rocket motor model. Commented the print statements in EOM and added a timer to calculate time spent logging data.
JMC: Cleanup - removing dead imports
JMC: Going to setup an example for the X-15 since there is a lot of public data.  Added a rocket motor model, which closes #2.  Updated the input file to reflect the XLR-99, which is the second, more powerful X-15 rocket.