Add --buildtime argument to support reproducible builds.
Add --buildtime argument to support reproducible builds.

To enable packages using pydoctor to build reproducibly, its output needs
to be the same from one build to another. Currently, pydoctor uses the
current time.

For more information about the motivation behind this change, please see
<https://wiki.debian.org/ReproducibleBuilds>.

Signed-off-by: Chris Lamb <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-lamb.co.uk>

jelmer/pydoctor,jelmer/pydoctor,jelmer/pydoctor