The copyright and license notice is already in the LICENSE file. There
is no justifiable reason to also require that it be included in every
file, since the individual files are not individually distributed except
as part of the entire package.
Currently, a child process does not emit the 'exit' event until 'close' events
have been received on all three of the child's stdio streams. This change makes
the child object emit 'exit' when the child exits, and a new 'close' event when
all stdio streams are closed.