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/package.json

@@ -0,0 +1,44 @@
+{
+  "name": "badge-maker",
+  "version": "3.3.1",
+  "description": "Shields.io badge library",
+  "keywords": [
+    "GitHub",
+    "badge",
+    "SVG",
+    "image",
+    "shields.io"
+  ],
+  "types": "index.d.ts",
+  "main": "lib/index.js",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/badges/shields.git",
+    "directory": "badge-maker"
+  },
+  "author": "Thaddée Tyl <thaddee.tyl@gmail.com>",
+  "license": "CC0-1.0",
+  "bugs": {
+    "url": "https://github.com/badges/shields/issues"
+  },
+  "homepage": "http://shields.io",
+  "bin": {
+    "badge": "lib/badge-cli.js"
+  },
+  "engines": {
+    "node": ">= 10",
+    "npm": ">= 5"
+  },
+  "collective": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/shields",
+    "logo": "https://opencollective.com/opencollective/logo.txt"
+  },
+  "dependencies": {
+    "anafanafo": "2.0.0",
+    "css-color-converter": "^2.0.0"
+  },
+  "scripts": {
+    "test": "echo 'Run tests from parent dir'; false"
+  }
+}