I don't think it's right to hardcode that ‘bundle’ name and use base64 here. A map file should be named the same as an output CSS file + '.map', saved in the same directory and sourceMappingURL directive should contain just a map name. SASS and LESS are already doing it as well. So should we move map file creation and sourceMappingURL adding [here](https://github.com/LearnBoost/stylus/blob/master/bin/stylus#L543) and [here](https://github.com/LearnBoost/stylus/blob/master/lib/renderer.js#L88)?