doc: add documentation about effectflag experiment

effectflag: split effect flag meta Split effect flag meta into 3 separate flags: - USERCHANGED - DATECHANGED - BRANCHCHANGED Also display them separately for the moment, they could be grouped back together if we want later.

tests: update missing amend (I need a hook)

template: update obsfate to be more human friendly Approach the obslog output for the moment.

template: add the obsfate template Reuse _getobsoletefate and nextvisiblesuccessors to easily get the obsolescence fate of any node. The limitation is that obsfate is as precise as these two functions, which is not great for nextvisiblesuccessors.

refactor: extract obs fate algorithm from _getobsoletereason Refactor _getobsoletereason to extract the obs fate computation into a separate function, it will be used later and put it in obshistory as it will be needed in other files. Rename _getobsoletereason to _getobsoletefateandsuccessors.

template: add successors template The successors templates display the closest visible successors of each changeset, we may have gap, like in this case: A -> B -> C -> D If we display A, C and D but not B, we can't display than B is the closest successor of A because it's not displayed. We display C as the closest successor of A instead.

template: add precursors template The precursors templates display the closest visible precursors of each changeset, we may have gap, like in this case: A -> B -> C If we display A and C but not B, we can't display than B is the closest precursor of C because it's not displayed. We display A as the closest precursor of C instead. Add a new test file as we will need to generate theses gaps and modifying test-evolve-obshistory.t will lead to many unrelated lines changes.

refactor: extract templates into a new file Extract evolve template from evolve/__init__.py to evolve/templatekw.py as more templates will come in the future.

obshistory: add the all option to obslog to show the while obs tree Add a --all option to obslog in order to display also the successors of each obs markers. It has the effect of showing a more comprehensive graph when a split or a divergence happened.