Add tengo support to RemoteNickFormat (#793)

This commit add support for using the result of a tengo script in RemoteNickFormat using {TENGO}
Also adds a new toml table [tengo] with key RemoteNickFormat and value location of the script.
This also moves the TengoModifyMessage from [general] to Message in [tengo]

Documentation:

RemoteNickFormat allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
The script will have the following global variables:
to modify: result
to read: channel, bridge, gateway, protocol, nick

The result will be set in {TENGO} in the RemoteNickFormat key of every bridge where {TENGO} is specified
The script is reloaded on every message, so you can modify the script on the fly.
Example script can be found in https://github.com/42wim/matterbridge/tree/master/contrib/remotenickformat.tengo

[tengo]
RemoteNickFormat="remotenickformat.tengo"

matterbridge.toml.sample

@@ -1480,6 +1480,7 @@ RemoteNickFormat="{NICK}"
 #The string "{PROTOCOL}" (case sensitive) will be replaced by the protocol used by the bridge
 #The string "{GATEWAY}" (case sensitive) will be replaced by the origin gateway name that is replicating the message.
 #The string "{CHANNEL}" (case sensitive) will be replaced by the origin channel name used by the bridge
+#The string "{TENGO}" (case sensitive) will be replaced by the output of the RemoteNickFormat script under [tengo]
 #OPTIONAL (default empty)
 RemoteNickFormat="[{PROTOCOL}] <{NICK}> "
 
@@ -1552,6 +1553,47 @@ IgnoreFailureOnStart=false
 #OPTIONAL (default empty)
 TengoModifyMessage="example.tengo"
 
+###################################################################
+#Tengo configuration
+###################################################################
+#More information about tengo on: https://github.com/d5/tengo/blob/master/docs/tutorial.md and
+#https://github.com/d5/tengo/blob/master/docs/stdlib.md
+
+[tengo]
+#Message allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
+#This script will receive every incoming message and can be used to modify the Username and the Text of that message.
+#The script will have the following global variables:
+#to modify: msgUsername and msgText
+#to read: msgChannel and msgAccount
+#
+#The script is reloaded on every message, so you can modify the script on the fly.
+#
+#Example script can be found in https://github.com/42wim/matterbridge/tree/master/gateway/bench.tengo
+#and https://github.com/42wim/matterbridge/tree/master/contrib/example.tengo
+#
+#The example below will check if the text contains blah and if so, it'll replace the text and the username of that message.
+#text := import("text")
+#if text.re_match("blah",msgText) {
+#    msgText="replaced by this"
+#    msgUsername="fakeuser"
+#}
+#OPTIONAL (default empty)
+Message="example.tengo"
+
+#RemoteNickFormat allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
+#The script will have the following global variables:
+#to modify: result
+#to read: channel, bridge, gateway, protocol, nick
+#
+#The result will be set in {TENGO} in the RemoteNickFormat key of every bridge where {TENGO} is specified
+#
+#The script is reloaded on every message, so you can modify the script on the fly.
+#
+#Example script can be found in https://github.com/42wim/matterbridge/tree/master/contrib/remotenickformat.tengo
+#
+#OPTIONAL (default empty)
+RemoteNickFormat="remotenickformat.tengo"
+
 ###################################################################
 #Gateway configuration
 ###################################################################