ST2 linter for R

Hi,

here is another suggestions for a possible future feature. Not sure whether my thoughts on an actual implementation are reasonable. Note that this would actually extend SublimeLinter (https://github.com/Kronuz/SublimeLinter) and not Rtools.

Here is how I think it could work:
1) The R package 'svTools' provides a lint function.
2) rpy2 provides a python interface to R (http://rpy.sourceforge.net/rpy2.html) so that it should be possible to call the lint function from python and work with the output.
3) The steps to add new languages to SublimeLinter are described on the bottom of this page: https://github.com/Kronuz/SublimeLinter

EDIT: Simple example

```
require(svTools)
# no lint warning
lint(text="summary(rnorm(100))")
# lint warning for additional )
lint(text="summary(rnorm(100)))")
# output:
# line column message type
#4 1 1 unexpected ')' error
```