Add support for Alpine Linux APKBUILD

[maxice8]

• Add handler for the output of atools
• Add linters for apkbuild-lint and secfixes-check from atools
• document support for apkbuild-lint and secfixes-check for apkbuild
• Make apkbuild_lint and secfixes_check default for apkbuild filetype
• Document new default linters for apkbuild
• Test default linters for apkbuild
• Add tests for atools handler, basic and dealing with Error and Warning
• Add document for apkbuild filetype

[maxice8]

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[maxice8]

Rebased

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[maxice8]

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[maxice8]

..

[maxice8]

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[maxice8]

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[maxice8]

[RyanSquared]

Please don't spam comments.

[RyanSquared]

LGTM 👍

I am not able to actively help contributing ATM but it looks fine.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[maxice8]

no

[hsanson]

ALE migrated from Travis to Github Actions (see #3548) so it is necessary to rebase this PR from latest master branch to trigger the required checks.

# Add dense-analysis as remote upstream on your local fork. Not 
# needed if already added.
git remote add upstream https://github.com/dense-analysis/ale.git

# Sync your local master with upstream master
git checkout master
git fetch upstream master
git merge upstream/master

# Rebase the PR branch with master
git checkout my-branch-name
git rebase master   # Fix any conflicts you may have

# Force push the updated PR branch to origin to trigger the checks
git push -f origin my-branch-name

[hsanson]

Looks good.