help: supporting both help and doc for aliases
This allows an alias to be definted like:
[alias]
lj = log -Tjson
lj:help = [-r REV]
lj:doc = Shows the revision log in JSON format.
Differential Revision: https://phab.mercurial-scm.org/D2678
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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
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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).