Wrap heading text in anchor tag and fixed subheading-anchor style

[FranciscoMoretti]

Clickable heading anchors

Headings were not linked previously because the anchor tag didn't wrap the header text.

By using the wrap behavior, the headers are clickable. Fixes #94

Headings anchor indicators

The css class subheading-anchor was not present in the project. I've created a simple style for subheading anchors. Feel free to suggest a different one.

To define the tailwind style in contentlayer.config.js I added that file to tailnwind.config.js content.

Info:

• Every file that has tailwind classes needs to be in the tailnwind.config.js content field.
• https://tailwindcss.com/docs/content-configuration

[vercel]

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