Fix a few warnings

src/activity_pub/activity.rs

@@ -11,12 +11,14 @@ impl Activity {
     }
 }
 
+#[allow(dead_code)]
 pub struct Create<'a, T, U> where T: Actor + 'static, U: Object {
     by: &'a T,
     object: U
 }
 
 impl<'a, T: Actor, U: Object> Create<'a, T, U> {
+    #[allow(dead_code)]
     pub fn new(by: &T, obj: U) -> Create<T, U> {
         Create {
             by: by,

src/activity_pub/sign.rs

@@ -1,7 +1,7 @@
 use base64;
 use hex;
 use chrono::Utc;
-use openssl::sha::{sha256, sha512};
+use openssl::sha::sha256;
 use serde_json;
 
 // (Comments are from the Mastodon source code, to remember what to do.)