Various Updates/Improvements

Fixed a couple mistakes in the gradient ascent algorithm, added a
"random_perf" option to calc_performance that determines whether the
covariance matrix is random or deterministic, added a
"plot_perf_samples" macro that shows a scatterplot of the current
performance vs temp and nutes (which is run at each iteration of
run_sim_gd, showing how parameters evolve over time), changed simulation
script names.