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/css-color-converter/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "css-color-converter",
+  "version": "2.0.0",
+  "description": "Converts CSS colors from one representation to another",
+  "main": "lib/index.js",
+  "scripts": {
+    "prepublish": "npm run lint && npm run build",
+    "lint": "eslint --ext .mjs src",
+    "build": "babel src -d lib",
+    "pretest": "npm run lint",
+    "test": "node src/__tests__/test.mjs"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/andyjansson/css-color-converter.git"
+  },
+  "keywords": [
+    "css",
+    "color",
+    "conversions",
+    "converter"
+  ],
+  "author": "Andy Jansson",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/andyjansson/css-color-converter/issues"
+  },
+  "homepage": "https://github.com/andyjansson/css-color-converter",
+  "dependencies": {
+    "color-convert": "^0.5.2",
+    "color-name": "^1.1.4",
+    "css-unit-converter": "^1.1.2"
+  },
+  "devDependencies": {
+    "@babel/cli": "^7.11.6",
+    "@babel/core": "^7.11.6",
+    "@babel/preset-env": "^7.11.5",
+    "eslint": "^7.9.0",
+    "eslint-config-airbnb-base": "^14.2.0",
+    "eslint-plugin-import": "^2.22.0"
+  }
+}