DeSheaToothakerIntroStats: Update for ggplot2 2.0.0

For Introductory Statistics for the Health Sciences, by Lise DeShea and Larry Toothaker (2015)

• The R package, ggplot2 is the major work horse behind our book's graphs. Version 2.0.0 of ggplot2 was released a few weeks ago, and we've updated the book's code so it works with the most current ggplot2. Historical versions of the book's code are available through the GitHub releases, as well as the Zenodo Archives. For the most part, the updated graphs will be indistinguishable from the ones in the book's hard cover.
• A few changes were made to the Rmd files to keep up with changes and improvements in knitr.
• Finally, the names of most files and directories were changes to be more URL-friendly. None of these should make references from the book obsolete though.