Refactor data flow to use streams

[mjp0]

Currently version of Datagram uses standard file system calls. To get more speed and avoid consuming memory like Chrome, we need streams. All internal parts support streams already, including encryption so this doesn't require major changes.

Only bigger question is the serialization which is done with msgpack right now.

---

Deliverables

• Refactor base set and get to streams
• Refactor encryption to use streams
• Refactor serialization to use streams