Add quote autocompletion for previous messages

Fixes https://github.com/profanity-im/profanity/issues/1649

Type `>` then press tab or shift tab to autocomplete previous messages,
then type your reply and send message.
Newlines are replaced with newline followed by `> `.
A newline is added at the end so that the user can immediately type a
message without manually adding a new line.

src/ui/privwin.c

@@ -82,6 +82,7 @@ privwin_incoming_msg(ProfPrivateWin* privatewin, ProfMessage* message)
     }
 
     wins_add_urls_ac(window, message);
+    wins_add_quotes_ac(window, message->plain);
 
     if (prefs_get_boolean(PREF_BEEP)) {
         beep();
@@ -99,6 +100,8 @@ privwin_outgoing_msg(ProfPrivateWin* privwin, const char* const message)
 {
     assert(privwin != NULL);
 
+    ProfWin* window = (ProfWin*)privwin;
+    wins_add_quotes_ac(window, message);
     win_print_outgoing((ProfWin*)privwin, "-", NULL, NULL, message);
 }