Use the site absolute url for twitter:image

[xerial]

#283 didn't truly fix the issue because Twitter requires absolute URLs for images.

This PR adds a new configuration micrositeUrl when we need to specify the site absolute url.

Alternative approaches:

• Setting site.url. But if we set this value in _config.yml, it makes difficult to see local images updates because there are many templates using {{site.url}} (e.g., favicon URLs), so all icon images refer remote server URLs.
• Using a twitter-card specific configuration (e.g., micrositeTwitterCardImageAbsoluteUrl)

With this fix, the card validator https://cards-dev.twitter.com/validator of Twitter icon can properly show the card image (/image/poster.png):

[manosbatsis]

Apologies for hijacking, but would it be possible to also fix og:image for linkedin in this PR? Not sure if an absolute URL is also needed here or if the format of og:image is not exactly correct - perhaps both name and property attributes are required - see details from linkedin post inspector bellow:

[xerial]

@manosbatsis Added fixes for Linked-in as well. I've added properties for og:image and og:title properties, and confirmed it's working well: https://www.linkedin.com/post-inspector/inspect/https:%2F%2Fwvlet.org%2Fairframe%2F

[manosbatsis]

That's fantastic, many thanks @xerial - looking forward to 0.7.26!

[calvellido]

Nice @xerial! Would you mind to add that new config parameter to the docs? Basically this file: settings.md

A simple description on why that parameter might be useful would suffice.

[xerial]

OK!

[xerial]

@calvellido Added a note to settings.md

[calvellido]

👏 👏 👏

[calvellido]

Just released 0.7.26 including these changes, thanks so much @xerial!

[manosbatsis]

Grand, thanks guys @calvellido and @xerial

[manosbatsis]

Hm, still can't see the new version on central after six hours or so. @calvellido this normal?

[juanpedromoreno]

It failed: https://travis-ci.org/47deg/sbt-microsites/jobs/457450111#L1488

I'll fix it.

[juanpedromoreno]

0.7.26 should be now on its way to Maven central.

[manosbatsis]

@juanpedromoreno confirmed, cheers

[calvellido]

Thanks @juanpedromoreno! 😘