Implement Deref<Target=UrlClient> for EsploraBlockchain

There is currently no way to access the client
from the EsploraBlockchain. This makes it difficult
for users to extend it's functionality. This PR exposes
both the reqwest and ureq clients. This PR is related to
PR #705.

src/blockchain/esplora/ureq.rs

@@ -14,6 +14,7 @@
 use std::collections::{HashMap, HashSet};
 use std::io;
 use std::io::Read;
+use std::ops::Deref;
 use std::time::Duration;
 
 #[allow(unused_imports)]
@@ -33,8 +34,9 @@ use crate::database::BatchDatabase;
 use crate::error::Error;
 use crate::FeeRate;
 
+/// Structure encapsulates ureq Esplora client
 #[derive(Debug, Clone)]
-struct UrlClient {
+pub struct UrlClient {
     url: String,
     agent: Agent,
 }
@@ -98,6 +100,14 @@ impl Blockchain for EsploraBlockchain {
     }
 }
 
+impl Deref for EsploraBlockchain {
+    type Target = UrlClient;
+
+    fn deref(&self) -> &Self::Target {
+        &self.url_client
+    }
+}
+
 impl StatelessBlockchain for EsploraBlockchain {}
 
 impl GetHeight for EsploraBlockchain {