Create R.sublime-completions

generated by running `ls(pattern="*", baseenv())` then weeding out non-alphanumeric-beginning commands (`:::`, `&.octmode`, etc.) and single-character commands (`T`, `q`, etc.). Finally, merged with http://dl.dropboxusercontent.com/u/2223411/R.sublime-completions (unknown author).
Merge pull request #17 from MattDMo/master

Create R.sublime-completions