Add Schema, Rewrite Protocol Structures & Interfaces and Revise Protocol Document

This pull request makes the following changes:

* Moved `architecture.graffle` and `architecture.pdf` under a `diagram` directory
* Removed version number from `architecture.graffle` and `architecture.pdf` - this is implicit by tag/reference number
* Created `schema/node.json` and `schema/payload.json` files conforming to JSON Schema
* Added table of contents to `protocol.md`
* Changed timestamp format requirement from ISO 8601 to RFC 3339 (a profile of ISO 8601)
* Added terms to terminology in `protocol.md` for "idempotent", "JavaScript Object Notation" and "JSON Schema"
* Completely rewrote Node Structure definitions in `protocol.md`
* Redefined Node Structures with JSON Schema
* Completely rewrote Payload Structure definitions in `protocol.md`
* Redefined Payload Structures with JSON Schema
* Replaced `author` object from journal and attributes with `originator` string for originator UUID
* Heavily revised journal, attributes and identity descriptions and merged within Payload Structures section
* Removed old External Interfaces section
* Added new set of GET requests to a new External Interfaces section
* Revised Internal Routines section

This pull request fixes #15 and #16