Add knitr and R markdown patterns to R.gitignore
These patterns handle cache diretories and temporary files created by the widely used [knitr](http://yihui.name/knitr/) and [R markdown](http://rmarkdown.rstudio.com/) packages.
J
jrnold committed
4956277b1ac108faad93c0fdc25f6b796dcb2cd8
Parent: ae5dd85