More intuitive subplot

Simple wrapper for Matlab's subplot. Most arguments get passed straight through. The only difference is in how the thisPlot index is handled. Instead of being a counter-intuitive 1D index, you just use 2D indices. For example, if you want a subregion from rows 3:4 and cols 4:5, just put {3:4 4:5}. If you want a single row/col region, just do {x y} or [x y].