REST-API: Merging/Rebasing with Mercurial?

As you may know we had a Google Summer of Code (GSoC) Project in 2015
that added a REST-API to roundup. I'd like to integrate this code.
The original announcement is at
https://sourceforge.net/p/roundup/mailman/message/34436352/
and there is also an issue in the tracker:
https://issues.roundup-tracker.org/issue2550734

If our version-control system was git I'd add a new remote to my
checkout of roundup, pull the repo above into a new local branch, rebase
to the current master and start fixing python3 compatibility issues and
adding documentation.

Can someone outline how to achieve this with mercurial?

Has there been some updates to this code since 2015 or did someone else
start integrating these changes? As far as I can see the project log
that was on bpaste is gone. Some content from the bpaste was copied to
the issue linked above. There is also some (html-only) documentation at
https://bitbucket.org/kinggreedy1991/restfulapidocumentation
which I don't understand how this works (this seems to be a web frontend
for the REST API of sorts)

Has someone been looking into this since? Anything I should know, I
think Ezio mentored this?

Thanks
Ralf
-- 
Dr. Ralf Schlatterbeck                  Tel:   +43/2243/26465-16
Open Source Consulting                  www:   http://www.runtux.com
Reichergasse 131, A-3411 Weidling       email: [email protected]