WIP: Support column and length information

First off, thanks for the great tool. :)

My Atom editor package [Atom-Lint](https://github.com/yujinakayama/atom-lint) supports `scss-lint` and basically it works fine. However currently `scss-lint` does not report the column and the length of the problems, so Atom-Lint always highlights the first character of each line in the editor as the following:

![Before](https://cloud.githubusercontent.com/assets/83656/2561495/5f1e2d02-b81a-11e3-8a51-dca9a09b780c.png)

This PR adds a basic support for column and length information:

![After](https://cloud.githubusercontent.com/assets/83656/2561499/8ab0202e-b81a-11e3-9f51-016a3564f153.png)

I think each linter needs specs to confirm the column range (though most of them seem to be fine), but I want to hear your thoughts first.

What do you think?