interledger-http API review for v1.0-rc

[gakonst]

interledger-http public items marked with x are documented. Non-exported items are not taken into account. Follows format from #561.

Part of #557.

• HttpAccount (trait)
• HttpStore (trait)
• deserialize_json (fn)
• HttpServer (struct)
  • as_filter(): Should we put some docs on the exact API endpoints this exposes or point to the spec?
• HttpClientService (struct)
  • Maybe document that send_request serializes (& oer encodes) the ILP packet before sending it to the next service?
• error (module)
  • Should we extract this to a separate crate? Seems generic enough, we discussed this another time.

[bstrie]

• as_filter: give a brief summary but link to the spec

[gakonst]

Yup, it does that right now: https://github.com/interledger-rs/interledger-rs/blob/master/crates/interledger-http/src/server.rs#L111. The used ilp_over_http method underneath also has details on how it works https://github.com/interledger-rs/interledger-rs/blob/master/crates/interledger-http/src/server.rs#L63