packaging: add Provides: python3-mercurial and Homepage to debian package
There are other packages that depend on python3-mercurial, like debian's
mercurial-git, so we should mark ourselves as providing it.
I compared the control file we generate to the one that the debian maintainers
generate, and noticed several differences:
- the Homepage bit. I included this, because why not
- a more robust Suggests list that includes a graphical merge tool
- a more robust Breaks list
- debian's Recommends openssh-client, we only Recommends ca-certificates
- a split into `mercurial` and `mercurial-common` (and possibly others?)
- a slightly different description
Differential Revision: https://phab.mercurial-scm.org/D9983
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).