Add save svg-badge directly to gist

This adds the posibility of saving an SVG badge generated by the same
shields.io dirictly to the gist. Instead of prepering a JSON file to
be sent to their service, we use their library directly, which outputs
an SVG file that we can save to the user’s gist.

Filenames ending in `.svg` will use this library automatically.

Additionally there is a major refactoring where the older `node:http`
library has been swapped out for `fetch`.

Also swap from node 16 to node 20

fixes #24

node_modules/char-width-table-consumer/README.md

@@ -0,0 +1,32 @@
+# char-width-table-consumer
+
+[![version](https://img.shields.io/npm/v/char-width-table-consumer.svg?style=flat-square)][npm]
+[![license](https://img.shields.io/npm/l/char-width-table-consumer.svg?style=flat-square)][npm]
+[![build](https://img.shields.io/circleci/project/github/metabolize/anafanafo.svg?style=flat-square)][build]
+[![code style](https://img.shields.io/badge/code_style-prettier-ff69b4.svg?style=flat-square)][prettier]
+[![lerna](https://img.shields.io/badge/maintained%20with-lerna-cc00ff.svg?style=flat-square)][lerna]
+
+[npm]: https://npmjs.com/char-width-table-consumer
+[build]: https://circleci.com/gh/metabolize/anafanafo/tree/master
+[prettier]: https://prettier.io/
+[lerna]: https://lernajs.io/
+
+Measure text using a character width table.
+
+[puppeteer]: https://pptr.dev/
+
+## Features
+
+This library allows efficient text measuring using a character width table.
+Create the tables using companion package [char-width-table-builder][].
+
+This performs a simple lookup, without considering kerning.
+
+Built with [Shields][] in mind.
+
+[char-width-table-builder]: https://www.npmjs.com/package/char-width-table-builder
+[shields]: https://github.com/badges/shields/
+
+## License
+
+This project is licensed under the MIT license.