Doc update.

Start reading from the recv channel earlier.

Simplified and debugged the filter logic.

Fixed another logic error, caused by a shadowed variable name.

Fixed some logic errors and initialized some things that needed to be initialized.

Removed some unused code.

Fixed reversed-logic error in checking for duplicate stanza extension types.

Address a bug that can happen if no SRV records can be found.

Pass the TLS config as a parameter to the Client constructor. Updated the example program.

Moved the tls.Config from a package-level variable to a client instance variable.

Use reflection instead of constructor functions to create extended stanza structures.

Renamed client.In and client.Out to Recv and Send, respectively.

Moved the library code into an xmpp directory.

Renamed examples to example, since there's only one program there.

Updated the example to match the new API, and fixed the roster Update to not require a reference to the client.