add alternating colors for rgroups

I hope I didn't overlook a much easier way to do this. I wanted to make the rgroups alternating in color rather than just setting the rgroupCSSstyle for the top rows. Added some examples to illustrate (and more importantly that nothing seems to break--rgroupCSSstyle and altcol can even be used together for more obnoxious coloring schemes).

I am also wondering if the main table row can be colored currently or if that would require further tweaking. Thanks so much for all the time I'm sure this package took. If only the doctors I work with were as coding/statistically savvy.