export everything from Internal module
handle code attribute in stanza errors

rfc 3920 allowed a "code" attribute in stanza errors. For compatibility,
we allow for (but ignore) it.
re-add debug output to outbound stanzas
fix some outdated comments
add support for extended attributes

See RFC6120 §8.4
( http://xmpp.org/rfcs/rfc6120.html#stanzas-extended )
add run tests

We lacked a test suite that even just tried connecting to a server and
bouncing a few stanzas back and forth. The "runtests" suite does just
that. It connects to 2 accounts on a server (set in a config
file ~/.pontarius-xmpp-tests/pontarius-xmpp-tests.conf) and tries
passing some messages and IQ stanzas back and forth. This should clear
the way for more interesting scenarios.