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/anafanafo/README.md

@@ -0,0 +1,40 @@
+# anafanafo
+
+[![version](https://img.shields.io/npm/v/anafanafo?style=flat-square)][npm]
+[![license](https://img.shields.io/npm/l/anafanafo?style=flat-square)][npm]
+[![build](https://img.shields.io/circleci/project/github/metabolize/anafanafo/main?style=flat-square)][build]
+[![bundle size](https://img.shields.io/bundlephobia/minzip/anafanafo?style=flat-square)][bundlephobia]
+[![code style](https://img.shields.io/badge/code_style-prettier-ff69b4?style=flat-square)][prettier]
+[![lerna](https://img.shields.io/badge/maintained%20with-lerna-cc00ff?style=flat-square)][lerna]
+
+[npm]: https://npmjs.com/anafanafo
+[build]: https://circleci.com/gh/metabolize/anafanafo/tree/main
+[bundlephobia]: https://bundlephobia.com/result?p=anafanafo
+[prettier]: https://prettier.io/
+[lerna]: https://lernajs.io/
+
+Efficiently compute text width in Verdana and Helvetica using
+[char-width-table-consumer][] and lookup tables.
+
+Built with [Shields][] in mind.
+
+(And because Verdana always makes me think of [this][the name game].)
+
+[char-width-table-consumer]: https://www.npmjs.com/package/char-width-table-consumer
+[shields]: https://github.com/badges/shields/
+[the name game]: https://www.youtube.com/watch?v=5MJLi5_dyn0
+
+## Usage
+
+```js
+const anafanafo = require('anafanafo')
+
+// Supports '11px Verdana', '10px Verdana', 'bold 10px Verdana', and 'bold 11px Helvetica'.
+const width = anafanafo('Shirley Shirley', { font: '11px Verdana' })
+```
+
+## License
+
+All rights to Verdana are owned by Microsoft Corp.
+
+The remainder of this project is licensed under the MIT license.