xmpp/oob d---------
all: generate disco features

Signed-off-by: Sam Whited <sam@samwhited.com>
oob: implement Marshaler and WriterTo

Implementing Marshaler and WriterTo for various types makes them much
more useful and sometimes more performant since the rest of the xmpp
module uses these interfaces heavily.

Signed-off-by: Sam Whited <sam@samwhited.com>
all: update copyright message

[ci skip]
all: remove use of session.Encoder method
stanza: move stanza functionality into new package
oob: Add some namespace constants
Add some structs for out of band data