Add a router to let developer subscribe to the stanza they are interested in #3
Description
The router should take inspiration from Go Fluux XMPP library: https://github.com/FluuxIO/go-xmpp/blob/master/router.go
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The router should take inspiration from Go Fluux XMPP library: https://github.com/FluuxIO/go-xmpp/blob/master/router.go