Package is deprecated

@ebressert - now that we have a release candidate for the merged ``astrodendro`` (formerly dendro-core) package, we should deprecate, remove, or rename our old repositories/forks to avoid confusion.

The new URLs are http://dendrograms.org and https://github.com/dendrograms/astrodendro

I've renamed mine and changed the README.md:

https://github.com/astrofrog/astrodendro-deprecated

and will eventually remove it.