Add build for Alpine 3.20

Fix manifest for new Alpine versions

Since the key is not imported with a repository definition, it needs to
be put in place explicitly.

Fix all memory issues

Fix invalid memory access

And free scanner when done.

Add build file for creating new Alpine repos

Keep building only for Alpine 3.19

New versions are no longer backwards compatible due Hare stdlib changes.

Adapt to Hare stdlib changes

Add build for releasing 3.18 packages

Add build manifest for new Alpine versions

Must be run manually once to create a repo for a new Alpine release.

Add .gitignore

Update README

Simplify interface to final intended form

Silence curl

Use intended final syntax for apk-index-update

Always read new index from stdin

Allow passing old index as positional argument.

Use more streaming for index merging

Use stdin for new index rather than old one

Remove stray ls in .build.yml

Automatically upload new version to repo

Using itself in the process... :)

First shot at CI build