tests: tell pip not to check for a newer version pip will check to see if it's the latest version, and complain if it isn't. The --no-index flag implies the --disable-pip-version-check flag, and makes the warning (and any associated network activity) go away.

changeset_templater: backport parts map of [templates] section from formatter

formatter: add support for parts map of [templates] section Unlike a mapfile whose template is looked up by spec -> mapfile -> topic, [templates] section is global. We use :sub-section syntax to define parts per template.

changeset_templater: backport separator template from formatter As commented, this should be used with docheader and docfooter, not with header nor footer. That's one reason why no props are passed to templater when rendering a separator. (See map-cmdline.changelog to understand what the "header" is.)

formatter: add support for separator template This seems useful for writing JSON template.

formatter: add support for docheader and docfooter templates templatepartsmap() is a minimal copy of changeset_templater.__init__(). I tried to factor out a common function, but it was unnecessarily complicated.