Generate the qemu.1 manpage using Sphinx; we do this with a new
top-level rst source file which is just the skeleton of the manpage
and which includes .rst.inc fragments where it needs to incorporate
sections from the larger HTML manuals.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200228153619.9906-30-peter.maydell@linaro.org