tendermint: impl fmt::UpperHex for abci::Transaction (#610)

Found myself wanting it today. I imagine you could use similar impls
throughout this crate, which allow you to do things like:

    println!("tx: {:X}", tx);

tendermint/src/abci/transaction.rs

@@ -3,11 +3,9 @@
 mod hash;
 
 pub use self::hash::Hash;
-use std::slice;
-use {
-    serde::{de::Error as _, Deserialize, Deserializer, Serialize, Serializer},
-    subtle_encoding::base64,
-};
+use serde::{de::Error as _, Deserialize, Deserializer, Serialize, Serializer};
+use std::{fmt, slice};
+use subtle_encoding::base64;
 
 /// Transactions are arbitrary byte arrays whose contents are validated by the
 /// underlying Tendermint application.
@@ -40,6 +38,12 @@ impl AsRef<[u8]> for Transaction {
     }
 }
 
+impl fmt::UpperHex for Transaction {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:X?}", self.as_bytes())
+    }
+}
+
 impl<'de> Deserialize<'de> for Transaction {
     fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
         let bytes = base64::decode(String::deserialize(deserializer)?.as_bytes())