Add autodoc website

[abhinav]

If this is not something you'd like for clap to provide, feel free to close the PR--it didn't require a lot of effort.

A preview of the output is available at https://abhinav.github.io/zig-clap/.

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This adds a zig build docs step that builds the documentation website and writes it to zig-out/docs.

It further includes a GitHub Workflow that publishes this website to GitHub Pages. The GitHub Workflow is divided into two jobs:

• build: builds the documentation and uploads it
• publish: downloads the documentation and publishes it

These are separate jobs to minimize permissions available to the build job.

This workflow runs on two events:

• after every push to master
• workflow_dispatch: this allows manually running the workflow from its Actions page if something went wrong

The instructions to do this came from the following sources:

• https://sudw1n.gitlab.io/posts/zig-build-docs/ provided instructions on how to build autodocs with Zig master.
• ziglibs/ansi-term#20 was used as reference for the GitHub Workflow.

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Important pre-merge steps:

If this PR is accepted, the following steps should be taken before merging the PR:

1. Go to Settings for the repository
2. Select Pages on the left under Code and automation
3. Under Build and deployment set Source to GitHub Actions
4. Merge the PR.

If the steps are missed, the PR will merge just fine, but the docs job will fail immediately on merge. This can be remedied by following steps 1-3 above, and either adding a new commit on master, or manually firing the workflow from the Actions > API Reference page.

[Hejsil]

Love it! I'll do the pre-merge steps and merge some time after Christmas :+1:

[Hejsil]

Looking good :+1: https://Hejsil.github.io/zig-clap