Add InvoicePayer and PaymentRetryHandler

When a payment fails, it's useful to retry the payment once the network
graph and channel scores are updated. InvoicePayer is a utility for
making payments which caches the payment Invoice so that it can be used
when retrying the payment. It is parameterized by a Payer and Router for
ease of customization and testing.

PaymentRetryHandler is used in connection with InvoicePayer. It is an
EventHandler decorator that intercepts PaymentFailed events and retries
that payment using the cached Invoice.

Author: jkczyz

lightning-invoice/Cargo.toml

@@ -13,6 +13,7 @@ bech32 = "0.8"
 lightning = { version = "0.0.99", path = "../lightning" }
 secp256k1 = { version = "0.20", features = ["recovery"] }
 num-traits = "0.2.8"
+bitcoin = "0.27"
 bitcoin_hashes = "0.10"
 
 [dev-dependencies]

lightning-invoice/src/lib.rs

@@ -15,11 +15,13 @@
 //!   * For parsing use `str::parse::<Invoice>(&self)` (see the docs of `impl FromStr for Invoice`)
 //!   * For constructing invoices use the `InvoiceBuilder`
 //!   * For serializing invoices use the `Display`/`ToString` traits
+pub mod payment;
 pub mod utils;
 
 extern crate bech32;
+extern crate bitcoin;
 extern crate bitcoin_hashes;
-extern crate lightning;
+#[macro_use] extern crate lightning;
 extern crate num_traits;
 extern crate secp256k1;