Scheduled events, connection, TLS handshake (with STARTTLS), read and write
on the socket are all done using only asyncio.

A lot of threads, and thread-related (and thus useless) things still remain.
This is only a first step.

71.

reload(sys) could cause problem in user code - ie, sys.stdout, excepthook, and displayhook would be reset, etc

Also, add detection of legacy XMPP version.

Fix see-other-host handling if no host is actually given. Also, limit number of consecutive redirection attempts.

Resolved by always normalizing JIDs to bare form, regardless of if they
are JID objects or strings.

Also simplified related code to prefer use of JID objects instead of
strings so they don't need to be parsed multiple times.

Remaining items are suitable default actions for language supporting
interfaces.

It is technically obsolete now, but remains because it set a default
subscription type of 'subscribe'.

Certificate host names are now matched (using DNS, SRV, XMPPAddr, and
Common Name), along with expiration check.

Scheduled event to reset the stream once the server's cert expires.

Handle invalid cert trust chains gracefully now.

The API registry generalizes the node handler system from the xep_0030
plugin so that other plugins can use it.

Plugins that are referenced as dependencies, but have not been
registered now will be imported. Newer plugins should register
themselves automatically, but older style plugins will be
explicitly registered after import.

The new system is backward compatible and will load older style plugins.

The new plugin framework allows plugins to track their dependencies, and
will auto-enable plugins as needed.

Dependencies are tracked via a class-level set named `dependencies` in
each plugin.

Plugin names are no longer tightly coupled with the plugin class name,
Pso EP8 style class names may be used.

Disabling plugins is now allowed, but ensuring proper cleanup is left to
the plugin implementation.

The use of a `post_init()` method is no longer needed for new style
plugins, but plugins following the old style will still require a
`post_init()` method.

The post_init() system can only reliably handle a single layer
of dependencies between plugins, but PEP plugins with XEP-0115
exceed that limit and plugins can be post_init'ed out of order. To
resolve this, we will special case XEP-0115 to be post_init'ed
first until the new plugin system with dependency tracking is
stable.

This would happen when receiving presence without a 'to' field, which
happens when receiving presence from other resources for the same account.

The exceptions are handled, so we don't need to clutter the output logs.