Project organization for specs

[muneeb-ali]

I was thinking that for a new person the blockstack-core/api folder is the most likely place where they'd expect to find the API docs.

I personally lost track of this doc.

Maybe we can move this spec there? If it makes sense, please start a pull request in the rc-0.14.1b branch.

Assigning @shea256 to move this forward or close the issue and CC'ing @larrysalibra, @jcnelson, and @csuwildcat.