Make 5aaf344472 changes without html tags

This is a great function, thanks! However, I think you introduced some html tags to the code in 5aaf344472, so the raw `rsquaredglm.R` can't be used directly.

I've copied your raw code from http://jonlefcheck.net/2013/03/13/r2-for-linear-mixed-effects-models/ (visited on 01/22/14) and made the changes on c03fd19.