Transaction broadcast (#209)

* Add transaction broadcast to all known peers once they have been
accepted by our own transaction pool.
* Some debug log

Fixes #200

pool/src/types.rs

@@ -163,6 +163,21 @@ pub trait BlockChain {
 	fn head_header(&self) -> Result<block::BlockHeader, PoolError>;
 }
 
+/// Bridge between the transaction pool and the rest of the system. Handles
+/// downstream processing of valid transactions by the rest of the system, most
+/// importantly the broadcasting of transactions to our peers.
+pub trait PoolAdapter: Send + Sync {
+	/// The transaction pool has accepted this transactions as valid and added
+	/// it to its internal cache.
+	fn tx_accepted(&self, tx: &transaction::Transaction);
+}
+
+/// Dummy adapter used as a placeholder for real implementations
+pub struct NoopAdapter {}
+impl PoolAdapter for NoopAdapter {
+	fn tx_accepted(&self, _: &transaction::Transaction) {}
+}
+
 /// Pool contains the elements of the graph that are connected, in full, to
 /// the blockchain.
 /// Reservations of outputs by orphan transactions (not fully connected) are