Add path_prefi and open_one_only options

Example configuration:

    {
        "open_one_only": true,
        "auto_extension" : [{
            "extension": ".scss",
            "prefix"   : "_"
        }, {
            "extension": ".coffee",
            "path_prefix"   : "node_modules/"
        }, {
            "extension": ".js",
            "path_prefix"   : "node_modules/"
        }, {
            "path_prefix"   : "node_modules/"
        }]
}