Additional documentation, including vignette, for Ostats_plot

[qdread]

Now that I have added some new features to Ostats_plot, I think it would be good to have a vignette that provides an example of all of them. I do not want to delay releasing the new package to CRAN, so I am going to go ahead and make the new release without the vignette. (We can always make yet another release when the vignette is done.) I hope to have some time in the near future to write the vignette (it can just be a very simple one with a bunch of plots) but if I do not get to it, anyone is welcome to work on it. I will make a new branch for it. Tagging @isafluck @sydnerecord @bbaiser !