Reexport RouteHintHop

Earlier @benthecarman re-exported `RouteHint` to make life-easier
for developpers that use `lightning-invoice` and don't use the
`lightning`-crate.

This only solved part of the issue. To create a `RouteHint` the
developer must also have access to `RouteHintHop`.

See also:
  PR #2572
	commit 79b426f

Author: ErikDeSmedt

lightning-invoice/src/lib.rs

@@ -74,7 +74,7 @@ use serde::{Deserialize, Deserializer,Serialize, Serializer, de::Error};
 #[doc(no_inline)]
 pub use lightning::ln::PaymentSecret;
 #[doc(no_inline)]
-pub use lightning::routing::router::RouteHint;
+pub use lightning::routing::router::{RouteHint, RouteHintHop};
 
 mod de;
 mod ser;