Add google-rlint as formatter for R

[dbarnett]

The google-rlint tool (https://code.google.com/p/google-rlint/) can reformat R code to the Google R Style Guide. We should add it as an available formatter for the r filetype.

[dbarnett]

BTW, the tool apparently doesn't support range formatting. Filed https://code.google.com/p/google-rlint/issues/detail?id=4

Another slight problem: No google-rlint tool… They created the repo but haven't pushed any code or file downloads to it: https://code.google.com/p/google-rlint/issues/detail?id=3