python: synchronize qemu.qmp documentation

python: synchronize qemu.qmp documentation

This patch collects comments and documentation changes from many commits
in the python-qemu-qmp repository; bringing the qemu.git copy in
bit-identical alignment with the standalone library *except* for several
copyright messages that reference the "LICENSE" file which is, for QEMU,
named "COPYING" instead and are therefore left unchanged.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>