ci: Add CI job for building the documentation

tutorial: compile the tutorial in rst so it can be included

tutorial: run the tutorial test file to update to latests ui messages

ignore: fix hgignore to point to the correct folder Files might have been imported initially as docs/training but were moved to docs/tutorial and the hgignore was likely forgotten.

stack: rename stack.revs into stack.indexedrevs They are accessible by an index, and are sorted. But they don't include all revisions for show in showstack().

stack: return from behindcount() early Reduces indentation.

stack: use self._revs in stack.behindcount() This code also doesn't care about the order of revisions, it just wants all revs except stack base, and that's what self._revs is.

stack: use self._revs in stack.heads() No code cares about the ordering of the heads anyway, so let's use the unordered property that doesn't need to be sliced (because it doesn't include base).

pick: Add a test to check that pick pick the right content

WIP on handling stacks