Find matching release ID for release-attachment

I've finally implemented the by-tag release matching thing. The info put
in on the command line actually gets used to attach files to the
release!

src/structs/release.rs

@@ -2,8 +2,8 @@ use serde::{Deserialize, Serialize};
 
 #[derive(Debug, Deserialize, Serialize)]
 pub struct Release {
-    id: usize,
-    tag_name: String,
+    pub id: usize,
+    pub tag_name: String,
     target_commitish: String,
     name: String,
     body: String,