Update additional head attributes

[daun]

Description

• Allow updating other attributes on the head element
• Filterable by string or regex: ['lang', 'dir', /^data-/]
• Default to lang and dir — the dir attribute is new
• I can imagine this still being a minor release: sites switching dir between pages must surely have implemented this feature on their own already, otherwise they'd be have broken layouts

Checks

• The PR is submitted to the master branch
• The code was linted before pushing (npm run lint)
• All tests are passing (npm run test)
• New or updated tests are included
• The documentation was updated as required

Additional information

Closes #50

[hirasso]

This is basically a copy of body-class-plugin, right?

Regarding bundle size, I'd vote in favour of marrying the two plugins at some point. But for now: Ship it 🚢

[daun]

@hirasso Yes! Exact copy. Let's hope that gzip compression works in favor of everyone using a bundler 🤠 If we end up using that code a third time, it's definitely time to re-architect 🤠 🤠