Proposal to add Ability to Delete Repo to index & registry API's and document cleanup

I have added a proposed API change to support deleting Repos in the index and registry API's. 

While I was at it, I made 2 new docs, one for the index API, and one for the registry API. This makes it much easier to see what their API's are, and the original document is now the spec document.

Please review and let me know what you think.

/cc @shykes @samalba