template: add minimal obsfate template function
The goal of this series is to have templates capable of displaying the
evolution of a changeset in a clean and human-readable way.
Add the succsandmarkers template return successors and markers so it can be
used separately like this:
> {succsandmarkers % "{get(succsandmarkers, "markers")|json};"}
The following patches will add template functions that takes successors and
markers as inputs and compute various obsfate fields from them.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).