Adding facets to genebar plot function

Updated plot function to allow users to modify aes() within ggplot. Update also includes a facet option, which likely need to be ruggedized so that only specific column names can be included (factors) or those that can be converted to happy facet columns.

I think this is about how far I can take it, and I'm thinking we can get this off to others to use. Most of the training material is in the readme file. Not sure if you think it should stay there or if we should pull that information out and direct people to a vignette.