Convert obsidian wiki links to markdown links

This is a modified version of markdown-it-wikilinks, modified to work with Obsidian style links.

This enables you to maintain your blog/digital garden in obsidian and publish via 11ty with github pages.

Some sites that use this:

• https://www.switchless.io/ (repo - https://github.com/switchless-io/docs)
• https://www.echoalex.com/ (repo - https://github.com/alexjv89/echoalex_com)