Use Ructe (#327)

All the template are now compiled at compile-time with the `ructe` crate.

I preferred to use it instead of askama because it allows more complex Rust expressions, where askama only supports a small subset of expressions and doesn't allow them everywhere (for instance, `{{ macro!() | filter }}` would result in a parsing error).

The diff is quite huge, but there is normally no changes in functionality.

Fixes #161 and unblocks #110 and #273

plume-models/src/comments.rs

@@ -68,26 +68,10 @@ impl Comment {
             .len() // TODO count in database?
     }
 
-    pub fn to_json(&self, conn: &Connection, others: &[Comment]) -> serde_json::Value {
-        let mut json = serde_json::to_value(self).expect("Comment::to_json: serialization error");
-        json["author"] = self.get_author(conn).to_json(conn);
-        let mentions = Mention::list_for_comment(conn, self.id)
-            .into_iter()
-            .map(|m| {
-                m.get_mentioned(conn)
-                    .map(|u| u.get_fqn(conn))
-                    .unwrap_or_default()
-            })
-            .collect::<Vec<String>>();
-        json["mentions"] = serde_json::to_value(mentions).expect("Comment::to_json: mention error");
-        json["responses"] = json!(
-            others
-                .into_iter()
-                .filter(|c| c.in_response_to_id.map(|id| id == self.id).unwrap_or(false))
-                .map(|c| c.to_json(conn, others))
-                .collect::<Vec<_>>()
-        );
-        json
+    pub fn get_responses(&self, conn: &Connection) -> Vec<Comment> {
+        comments::table.filter(comments::in_response_to_id.eq(self.id))
+            .load::<Comment>(conn)
+            .expect("Comment::get_responses: loading error")
     }
 
     pub fn update_ap_url(&self, conn: &Connection) -> Comment {