topics: add tests for cases when a topic is empty

readme: mention compatibility with future 4.4

topic: update the message used with --age for empty topic This clarify things when a topic got emptied by publishing.

sharing: edit pass

user-guide: edit pass

topic: stabilise the output of --age when date ties We just needed to introduce sort to stabilize the output order.

tests: update after removing of redundant amend commit Following e8a7c1a0565a, temporary amend commits has been removed impacting all revision numbers in tests including amend operations. Update tests case to use description or hashes when possible and update revisions number when not.

topic: setup 'topic' value for working ctx The way amend work in core change in e8a7c1a0565a. The intermediate commit disappear and we can no longer rely on it to carry the topic value to amend. To fix this, we ensure the current topic value can be retrieved through the `workingctx.extra()` value. Since there is no way to carry a "missing" key information in a way that survives and "dict.update" call. We also has to introduce hacking behavior about a special empty value for topic.

tests: abstract version number for test-topic-stack.t Using explicite version number always bring trouble, this is why we have unique description that can select changesets.

evolve: use registrar.templatekeyword to register template keyword functions Now, using registrar.templatekeyword of Mercurial directly in evolve extension should be safe enough. because it has been available since Mercurial 3.8, and minimum Mercurial version for evolve extension is 3.8, too. BTW, this also fixes an issue of "hg help templates" output that template keywords "precursors" and "successors" are not displayed as same as others, because they do not have ":KEYWORD:" prefix in their docstring.

evolve: use registrar.revsetpredicate to register revset predicate functions Now, using registrar.revsetpredicate of Mercurial directly in evolve extension should be safe enough. because it has been available since Mercurial 3.8, and minimum Mercurial version for evolve extension is 3.8, too.

topic: use registrar.revsetpredicate to register revset predicate functions Now, using registrar.revsetpredicate of Mercurial directly in topic extension should be safe enough. because it has been available since Mercurial 3.8, and minimum Mercurial version for topic extension is 4.0. This patch also removes modsetup() in topic/revset.py, because it is useless. BTW, this patch fixes an issue of "hg help revsets" output that custom revset predicates are not displayed as same as others, because they are not "inline literal" in reST syntax (``NAME``).

doc: make paragraphs before example code end with "::" for reST syntax This prevents lines in an example code from being treated as a part of normal paragraph. For issue example, lines are folded into one paragraph.

topic: centralize compatibility logic between hg versions into compat module This patch can delay loading obsutil and obsolete modules until they are actually used at "hg topics" or so, if demandimport of Mercurial is enabled.

readme: mention the improvement to stack in the readme

test: issue a clarifying graph print in tests/test-stack-branch.t