Added pcolor_cmap option.

I was snooping around to see if there was a way to set the cmap of pcolor, and I couldn't find anything. I've added a very simplistic way to do this (kwarg: 'pcolor_cmap' ). As it stands it works fairly well, with one exception. There is a sliver of whitespace between the end of pcolor and the plot window. I will look into fixing this by passing something to the 'extent' parameter of pcolor.

It would also be cool to have a colorbar for pcolor (even if the pcolor cmap is grayscale), as one sometimes wishes to see the values of the loglikelihood function (which I believe is what the color represents; correct me if I'm wrong on this).