feat: add config attribute extends

[Shinigami92]

Short description of what this resolves:

We want to support a extendable configuration file
So we introduce a new configuration attribute extends that behave like eslint's extends

Proposed changes:

• Add new attribute extends in configuration

---

Tasks:

• add extension ruleset map
• read new configuration structure
• pass config through to verify
• add tests
• define recommended ruleset

[Shinigami92]

@thedaviddias Ready for review! 🎉

At first, you can only focus on changes to the source files
Then, if you want, also look at the test files

We are getting closer to the release of version 1.0.0 😃

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Schweinepriester]

This was automatically closed without conclusion; extendable configuration is still desirable imho.

[codecov]

Codecov Report

Merging #489 (59d55ca) into beta (e459672) will not change coverage.
The diff coverage is n/a.

❗ Current head 59d55ca differs from pull request most recent head a763b2e. Consider uploading reports for the commit a763b2e to get more accurate results

@@     Coverage Diff     @@
##   beta   #489   +/-   ##
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[gitrequests]

Configuration merge is still not available?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Schweinepriester]

Still think this is very desirable, shouldn't be closed and get keep-unstale.

[ghaschel]

No news on this? This is a must-have feature in every linter imho.

[donroyco]

Any update on this PR? It would be really helpful when this functionality lands in HTMLHint.

[Kristinita]

Are there any chances that this feature will be implemented to HTMLHint?

Thanks.