Deep share document part

[syakunin]

One can want to share only a portion of his document without revealing the whole document. In this case deep share functionality can accept document path, re-encrypt and share document part only, which is under the specified path. For example:

Alice have this document:

{
  "documents": {
	 "topSecret": ["CID100", "CID101", "CID102"],
  },
  "photos": {
	  "wedding": ["CID1", "CID2", "CID3"],
  }
}

and she wants to share only wedding part of the document with Bob, so she might call:

const scid = context.secure(ipfs).deepShare(cid, bobPublicKey, '/photos/wedding');

The context should traverse the path, extract specified document part, encrypt it and return document SCID which Alice can pass to Bob.