Add support for Harmony (#1656)

Harmony is a relatively new (1,5yo) chat protocol with a small community.
This introduces support for Harmony into Matterbridge, using the functionality
specifically designed for bridge bots. The implementation is a modest 200 lines
of code.

matterbridge.toml.sample

@@ -1660,6 +1660,18 @@ StripNick=false
 #OPTIONAL (default false)
 ShowTopicChange=false
 
+###################################################################
+# Harmony
+###################################################################
+
+[harmony.chat_harmonyapp_io]
+Homeserver = "https://chat.harmonyapp.io:2289"
+Token = "your token goes here"
+UserID = "user id of the bot account"
+Community = "community id that channels will be located in"
+UseUserName = true
+RemoteNickFormat = "{NICK}"
+
 ###################################################################
 #API
 ###################################################################
@@ -1953,6 +1965,10 @@ enable=true
     account="zulip.streamchat"
     channel="general/topic:mytopic"
 
+    [[gateway.inout]]
+    account="harmony.chat_harmonyapp_io"
+    channel="channel id goes here"
+
     #API example
     #[[gateway.inout]]
     #account="api.local"