You can clone with
HTTPS or Subversion.
We at Metabroadcast have implemented secondary direct and inverted indexes on top of Astyanax, and would be glad to contribute it as a recipe.
Here's a blog post describing our approach and linking to our open source implementation: http://metabroadcast.com/blog/enhancing-cassandra-powers-with-secondary-indexes
If it's okay for you, I'll do all the work to arrange it as a pull request.
Please submit a pull request.