Some initial benchmarks and utilities, including keplerian elements. More typed coordinate stuff to come

Cargo.toml

@@ -30,3 +30,11 @@ approx = "0.5"
 serde_json = "1.0"
 criterion = "0.7"
 num-dual = "0.15"
+
+[[bench]]
+name = "kepler"
+harness = false
+
+[[bench]]
+name = "propagation"
+harness = false