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We have two basic example commands. But it’s not entirely finished because
there are some error checks that we don’t do.

ref #2521

Explain that the behaviour is otherwise undefined, in the comment.

The generated XML is very verbose because each IRC formatting tag makes us
close a <span/> element and reopen it with the new style applied.  However,
this works quite well and is easy to implement.

And now we handle namespaces, yay.
And a nice little test.

Also correctly respond to PING with the id, escape some XML content, but not
always

Generate events on stanza and stream open/close.
Create Stanza and serialize them.

Note: XML namespaces are not handled yet.