Keep clodius docs under clodius

The clodius docs are currently in the [higlass repo](https://github.com/higlass/higlass/blob/develop/docs/data_preparation.rst). They should be moved here, and a sphinx build should be set up, with the results pushed to an S3 bucket. Once it's in place, a least [one inbound link](https://github.com/higlass/higlass/blob/develop/docs/track_types.rst#2d-rectangle-domain) should be fixed.

@pkerpedjiev : Could you confirm that this is what you want? I'm also wondering if that complexity is really necessary. I guess you wanted a distinction between the release docs and the under-construction docs, but I feel that just looking at the markdown on github on the branch you prefer does that well enough.