Add GitHub Pages documentation deployment

[Copilot]

The repository lacked a public documentation site for prospective users to preview the API.

Changes

• GitHub Actions workflow (.github/workflows/documentation.yml): Builds Swift DocC documentation on macOS, converts to static HTML, deploys to Pages on push to master
• README update: Added documentation link to https://mikelrob.github.io/Animations/documentation/animations/
• Setup guide (GITHUB_PAGES_SETUP.md): Instructions for repository owner to enable Pages with "GitHub Actions" source

Activation Required

Repository owner must enable GitHub Pages in Settings → Pages → Source: "GitHub Actions" for deployment to function.

Original prompt

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This section details on the original issue you should resolve

<issue_title>No GitHub pages</issue_title>
<issue_description>This repo doesn't have a GitHub pages page. It should have it's docs deployed to GitHub pages for prospective users to preview.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes No GitHub pages #8

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