Address this issue: merge pelican-open_graph plugin into SEO plugin.

What's Changed

• Improve content rewriting by @patrickfournier in #77
• Enhance OpenGraph tags by @patrickfournier in #78
• Add OpenGraph tags for Article content by @patrickfournier in #79

New Contributors

• @patrickfournier made their first contribution in #77

Full Changelog: 1.4.0...1.5.0

Add setting to add site map to robots.txt

Support SITEURL values that contain slugs after the domain

• Add ability to configure the plugin via the Pelican settings file

Improve test for canonical feature and update linters.

Fix addition of undesirable white space in HTML because of BeautifulSoup.prettify()

Add support for external canonical URL. Refs #33.

Open Graph and Twitter Cards support

Fix definitively encoding issues when open file

Fix schemas generated in wrong script tags