Split monero-harness into harness and rpc

This allows us to move `monero-harness` and `bitcoin-harness` into
`[dev-dependencies]` of `swap`.

monero-rpc/src/lib.rs

@@ -0,0 +1,17 @@
+#![warn(
+    unused_extern_crates,
+    missing_debug_implementations,
+    missing_copy_implementations,
+    rust_2018_idioms,
+    clippy::cast_possible_truncation,
+    clippy::cast_sign_loss,
+    clippy::fallible_impl_from,
+    clippy::cast_precision_loss,
+    clippy::cast_possible_wrap,
+    clippy::dbg_macro
+)]
+#![forbid(unsafe_code)]
+
+mod rpc;
+
+pub use self::rpc::*;