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/char-width-table-consumer/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "char-width-table-consumer",
+  "version": "1.0.0",
+  "repository": "metabolize/anafanafo",
+  "description": "Measure text using a character width table",
+  "main": "src",
+  "scripts": {
+    "test": "jest"
+  },
+  "author": "Metabolize",
+  "license": "MIT",
+  "dependencies": {
+    "binary-search": "^1.3.5"
+  },
+  "gitHead": "4bd230d372ffe93cd9bf7f036b83be6ef5dab75e"
+}