feat: improve ergonomics for serialization format

Goal: To make the serialization format more sensible instead of it being a reflection of our internal (ie private) data model.

- mostly handled with #[serde()] macros (renaming, flattening)
- renamed NetworkCoordinate::position to heightvec which is a better name, even if not seen in the published interface
- changed HeightVector from a tuple struct to a named struct so we can control serde on a field-by-field basis
- updated README, tests, and doc tests to match

Signed-off-by: Stephen Waits <steve@waits.net>

src/lib.rs

@@ -51,7 +51,7 @@
 //!
 //! // mock up a remote NC for the sake of this example (normally the node would actually receive
 //! // this from a remote node)
-//! let received_msg = "{\"position\":[{\"inner\":[1.5,0.5,2.0]},0.1],\"error\":1.0}";
+//! let received_msg = "{\"position\":[1.5,0.5,2.0],\"height\":0.1,\"error\":1.0}";
 //! let remote_nc: NetworkCoordinate<3> = serde_json::from_str(received_msg).unwrap();
 //!
 //! // mock up a measured RTT between us and that node (normally the nodes would coordinate
@@ -77,7 +77,7 @@
 //!
 //! // mock up a remote NC for the sake of this example (normally the node would actually receive
 //! // this from a remote node)
-//! let received_msg = "{\"position\":[{\"inner\":[1.5,0.5,2.0]},0.1],\"error\":1.0}";
+//! let received_msg = "{\"position\":[1.5,0.5,2.0],\"height\":0.1,\"error\":1.0}";
 //! let remote_nc: NetworkCoordinate<3> = serde_json::from_str(received_msg).unwrap();
 //!
 //! // estimate the RTT to this remote node without measuring it directly