pyoxidizer: update to PyOxidizer 0.9
We were previously using a Git commit from a few days before the 0.8
release. This commit upgrades us to the just-released 0.9 release.
This required some Starlark changes due to backwards incompatible
changes.
Differential Revision: https://phab.mercurial-scm.org/D9228
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.