Add a `.no-sublime-package` file, fixes ST3 compatibility

- this causes the plugin to be installed as it would be in Sublime Text 2 (as a folder, rather than a zipped file)
- fixes #68

Source of fix: [News - Package Control](https://sublime.wbond.net/news#2013-08-09-Package_Control_2)

> Proper package installation in ST3 via `.sublime-package` files. This allows users to override individual files in a package with their own version. Packages that must be unpacked simply need to have a file named `.no-sublime-package` in the root of the package.