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/badge-maker/README.md

@@ -0,0 +1,142 @@
+# badge-maker
+
+[![npm version](https://img.shields.io/npm/v/badge-maker.svg)](https://npmjs.org/package/badge-maker)
+[![npm license](https://img.shields.io/npm/l/badge-maker.svg)](https://npmjs.org/package/badge-maker)
+[![npm type definitions](https://img.shields.io/npm/types/badge-maker)](https://npmjs.org/package/badge-maker)
+
+## Installation
+
+```sh
+npm install badge-maker
+```
+
+## Usage
+
+### On the console
+
+```sh
+npm install -g badge-maker
+badge build passed :green > mybadge.svg
+```
+
+### As a library
+
+With CommonJS in JavaScript,
+
+```js
+const { makeBadge, ValidationError } = require('badge-maker')
+```
+
+With ESM or TypeScript,
+
+```ts
+import { makeBadge, ValidationError } from 'badge-maker'
+```
+
+```js
+const format = {
+  label: 'build',
+  message: 'passed',
+  color: 'green',
+}
+
+const svg = makeBadge(format)
+console.log(svg) // <svg...
+
+try {
+  makeBadge({})
+} catch (e) {
+  console.log(e) // ValidationError: Field `message` is required
+}
+```
+
+### Node version support
+
+The latest version of badge-maker supports all currently maintained Node
+versions. See the [Node Release Schedule][].
+
+[node release schedule]: https://github.com/nodejs/Release#release-schedule
+
+## Format
+
+The format is the following:
+
+```js
+{
+  label: 'build',  // (Optional) Badge label
+  message: 'passed',  // (Required) Badge message
+  labelColor: '#555',  // (Optional) Label color
+  color: '#4c1',  // (Optional) Message color
+
+  // (Optional) One of: 'plastic', 'flat', 'flat-square', 'for-the-badge' or 'social'
+  // Each offers a different visual design.
+  style: 'flat',
+}
+```
+
+## Colors
+
+There are three ways to specify `color` and `labelColor`:
+
+1. One of the [Shields named colors](./lib/color.js):
+
+- ![][brightgreen]
+- ![][green]
+- ![][yellow]
+- ![][yellowgreen]
+- ![][orange]
+- ![][red]
+- ![][blue]
+- ![][grey] ![][gray] – the default `labelColor`
+- ![][lightgrey] ![][lightgray] – the default `color`
+
+- ![][success]
+- ![][important]
+- ![][critical]
+- ![][informational]
+- ![][inactive] – the default `color`
+
+2. A three- or six-character hex color, optionally prefixed with `#`:
+
+- ![][9cf]
+- ![][#007fff]
+- etc.
+
+3. [Any valid CSS color][css color], e.g.
+
+- `rgb(...)`, `rgba(...)`
+- `hsl(...)`, `hsla(...)`
+- ![][aqua] ![][fuchsia] ![][lightslategray] etc.
+
+[brightgreen]: https://img.shields.io/badge/brightgreen-brightgreen.svg
+[success]: https://img.shields.io/badge/success-success.svg
+[green]: https://img.shields.io/badge/green-green.svg
+[yellow]: https://img.shields.io/badge/yellow-yellow.svg
+[yellowgreen]: https://img.shields.io/badge/yellowgreen-yellowgreen.svg
+[orange]: https://img.shields.io/badge/orange-orange.svg
+[important]: https://img.shields.io/badge/important-important.svg
+[red]: https://img.shields.io/badge/red-red.svg
+[critical]: https://img.shields.io/badge/critical-critical.svg
+[blue]: https://img.shields.io/badge/blue-blue.svg
+[informational]: https://img.shields.io/badge/informational-informational.svg
+[grey]: https://img.shields.io/badge/grey-grey.svg
+[gray]: https://img.shields.io/badge/gray-gray.svg
+[lightgrey]: https://img.shields.io/badge/lightgrey-lightgrey.svg
+[lightgray]: https://img.shields.io/badge/lightgray-lightgray.svg
+[inactive]: https://img.shields.io/badge/inactive-inactive.svg
+[9cf]: https://img.shields.io/badge/9cf-9cf.svg
+[#007fff]: https://img.shields.io/badge/%23007fff-007fff.svg
+[aqua]: https://img.shields.io/badge/aqua-aqua.svg
+[fuchsia]: https://img.shields.io/badge/fuchsia-fuchsia.svg
+[lightslategray]: https://img.shields.io/badge/lightslategray-lightslategray.svg
+[css color]: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value
+[css/svg color]: http://www.w3.org/TR/SVG/types.html#DataTypeColor
+
+## Raster Formats
+
+Conversion to raster formats is no longer directly supported. In javascript
+code, SVG badges can be converted to raster formats using a library like
+[gm](https://www.npmjs.com/package/gm). On the console, the output of `badge`
+can be piped to a utility like
+[imagemagick](https://imagemagick.org/script/command-line-processing.php)
+e.g: `badge build passed :green | magick svg:- gif:-`.