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/color-name/package.json

@@ -0,0 +1,28 @@
+{
+  "name": "color-name",
+  "version": "1.1.4",
+  "description": "A list of color names and its values",
+  "main": "index.js",
+  "files": [
+    "index.js"
+  ],
+  "scripts": {
+    "test": "node test.js"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git@github.com:colorjs/color-name.git"
+  },
+  "keywords": [
+    "color-name",
+    "color",
+    "color-keyword",
+    "keyword"
+  ],
+  "author": "DY <dfcreative@gmail.com>",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/colorjs/color-name/issues"
+  },
+  "homepage": "https://github.com/colorjs/color-name"
+}