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/LICENSE

@@ -0,0 +1,20 @@
+The MIT License (MIT)
+
+Copyright 2015 Andy Jansson <andyjansson@users.noreply.github.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.