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-convert/CHANGELOG.md

@@ -0,0 +1,4 @@
+# 0.5.3 - 2015-06-02
+
+- Fixed: hsl2hsv does not return `NaN` anymore when using `[0,0,0]`
+([#15](https://github.com/harthur/color-convert/issues/15))