Manage server load without dropping readings

[ambergristle]

As a relay, Demeter is only useful if it ensures all data is captured.

What

• A retry layer to prevent network issues from swallowing data.
• A queue to prevent data loss in the case of server overload?
  • Essentially offloading call/retry to server. How useful is this, really?

Considerations

• What to do with Readings? #3
• What happens if the callback fails? Repeatedly?
• What happens if Demeter goes down? And can't be restored?
• Is Demeter responsible for tracking clients?