function finish(err, root){
        if(!callback)
            return;
        var cb = callback;
        callback = null;
        cb(err, root);
    }
Resolves the path of an imported file, relative to the importing origin.
This method exists so you can override it with your own logic in case your imports are scattered over multiple directories.
@function
@param {string} origin The file name of the importing file
@param {string} target The file name being imported
@returns {string|null} Resolved path to `target` or `null` to skip the file