Implement list

Allow users to query all the available emotes using the new special
emote reference "list". Replace the legacy GitHub link with a reference
to this command.

Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>

plugin.py

@@ -157,9 +157,13 @@ class UnicodeEmoji(callbacks.Plugin):
     def e(self, irc, msg, args, emote):
         """<emote>
 
-        Prints the Unicode emoji as listed here https://gist.github.com/mogad0n/476c3880dc0e0a059ed03efa265e50f7
+        Prints the Unicode emoji as listed with `!e list`
         """
 
+        if emote == 'list':
+            irc.reply(', '.join(emoji.keys()), msg=msg, prefixNick=False)
+            return
+
         re = emoji.get(emote.lower())
         if re is None:
             re = emoji['fuck-off']