Re-export lightning-invoice as bolt11-invoice from lightning

Now that `lightning` depends on `lightning-invoice`, we should
re-export it like we do `bitcoin` and `types`.

Author: TheBlueMatt

lightning/src/lib.rs

@@ -54,6 +54,9 @@ extern crate alloc;
 pub extern crate lightning_types as types;
 
 pub extern crate bitcoin;
+
+pub extern crate lightning_invoice as bolt11_invoice;
+
 #[cfg(any(test, feature = "std"))]
 extern crate core;