Transfer Function Utilities for V4.2

Collection of utilities I found useful when doing traditional bode diagram control system analysis.

When doing traditional bode diagram control system analysis of ill-conditioned high order SISO systems in V4.2 with Control System Toolbox, I found using these utilities improved the robustness of my results. There's also a nice function to plot an approximate (asymptotic) bode diagram which I find helps me visualise a transfer function's poles and zeros slightly better than with an exact bode diagram. Note also that Control System Toolbox's bode.m was a contributing file but I couln't figure out how to acknowledge it.