Add support for rendering highlights with comments

This commit implements rendering comments from the `["comment",
<COMMENT_TEXT>]` tag in a highlight note.

Comment contents get rendered like a kind 1 note's "content" field

This commit also adds the `r` "reference" tag as a standard tag reference type

Changelog-Added: Add support for rendering highlights with comments
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damus/Models/CommentItem.swift

@@ -0,0 +1,23 @@
+//
+//  CommentItem.swift
+//  damus
+//
+//  Created by Daniel D’Aquino on 2024-08-14.
+//
+
+import Foundation
+
+struct CommentItem: TagConvertible {
+    static let TAG_KEY: String = "comment"
+    let content: String
+    var tag: [String] {
+        return [Self.TAG_KEY, content]
+    }
+    
+    static func from_tag(tag: TagSequence) -> CommentItem? {
+        guard tag.count == 2 else { return nil }
+        guard tag[0].string() == Self.TAG_KEY else { return nil }
+        
+        return CommentItem(content: tag[1].string())
+    }
+}

damus/Models/Contacts+.swift

@@ -109,7 +109,7 @@ func is_already_following(contacts: NostrEvent, follow: FollowRef) -> Bool {
         case let (.pubkey(pk), .pubkey(follow_pk)):
             return pk == follow_pk
         case (.hashtag, .pubkey), (.pubkey, .hashtag),
-            (.event, _), (.quote, _), (.param, _), (.naddr, _):
+            (.event, _), (.quote, _), (.param, _), (.naddr, _), (.reference(_), _):
             return false
         }
     }