Add fractions of seconds to <delay/> timestamps

Include fractions of a second with XEP-0203 <delay/> timestamps, as
specified in XEP-0082.

	Old timestamp: 2014-05-19T11:55:00Z
	New timestamp: 2014-05-19T11:55:00.123Z
Let jlib use "B" instead of "w" to format integers

As a small optimization, use io:format/2's "B" control sequence to
format integers.  We don't need to have the Erlang VM figure out the
data type if we already know it.