Add xrefcheck

[gromakovsky]

Description

Use the xrefcheck tool to ensure that cross-references are valid.

Related issues(s)

None

✓ Checklist for your Pull Request

Ideally a PR has all of the checkmarks set.

If something in this list is irrelevant to your PR, you should still set this checkmark indicating that you are sure it is dealt with (be that by irrelevance).

• [x] I made sure my PR addresses a single concern, or multiple concerns which are inextricably linked. Otherwise I should open multiple PR's.
• [x] If your PR fixes/relates to an open issue then the description should reference this issue. See also auto linking on github.

Related changes (conditional)

• Tests

  • [x] If I added new functionality, I added tests covering it.
  • [x] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  I checked whether I should update the docs and did so if necessary:

  • [x] README
  • [x] Haddock

• Record your changes

  • [x] I added an entry to the changelog if my changes are visible to the users and
  • [x] provided a migration guide for breaking changes if possible

Stylistic guide (mandatory)

• [x] My commit history is clean (only contains changes relating to my issue/pull request and no reverted-my-earlier-commit changes) and commit messages start with identifiers of related issues in square brackets.

  Example: [#42] Short commit description

  If necessary both of these can be achieved even after the commits have been made/pushed using rebase and squash.

[gromakovsky]

Ah, I guess I should make this check optional. I am considering switching CI to GitHub actions, so maybe I'll do that first.

[Martoon-00]

Mda, 6 jobs each resolving all refs to issues located in CHANGES.md. 429 guaranteed, need to do something with this soon.

Probably it's worth enabling retry: https://docs.travis-ci.com/user/common-build-problems/#travis_retry

[gromakovsky]

Doing it in 6 jobs definitely does not make sense. I'd like to try GitHub actions first before doing it properly.

[Martoon-00]

Ah right, I see

[gromakovsky]

I might end up doing xrefcheck-action and using it here before considering this PR done.

[gromakovsky]

Alright, I think all issues are resolved and it works pretty nicely now.

[gromakovsky]

I've also bumped the version to 1.7.0 because I want to make a new release and don't want to make another PR for that.

[Martoon-00]

Since you are going to make a release, may I quickly add one small PR? Wanna have it soon

[Martoon-00]

I was wrong, that issue is already resolved. Let's make a release :)

[gromakovsky]

Great!