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/README.md

@@ -0,0 +1,92 @@
+# css-color-converter [![Build Status][ci-img]][ci]
+
+Converts CSS colors from one representation to another 
+
+[ci-img]:  https://travis-ci.org/andyjansson/css-color-converter.svg
+[ci]:      https://travis-ci.org/andyjansson/css-color-converter
+
+## Installation
+
+```js
+npm install css-color-converter
+```
+
+## Usage
+
+**Example usage**: 
+```js
+import { fromString } from 'css-color-converter';
+
+fromString('rgb(255, 255, 255)').toHslString(); // hsl(0, 0%, 100%)
+fromString('rgba(255, 255, 255, 0.5)').toHslString(); // hsla(0, 0%, 100%, 0.5)
+fromString('blue').toRgbString(); // rgb(0, 0, 255)
+fromString('red').toHexString(); // #ff0000
+```
+## Functions
+
+### `fromString(str)`
+| parameter | type   | description                                    |
+| --------- | ------ | ---------------------------------------------- |
+| `str`     | string | Supports named colors, hex, rgb/rgba, hsl/hsla |
+
+**Returns** [`instance`](#Methods) if valid, `null` if invalid.
+
+### `fromRgb([r, g, b])`
+
+| parameter | type   | description   |
+| --------- | ------ | ------------- |
+| `r`       | int    | red (0-255)   |
+| `g`       | int    | green (0-255) |
+| `b`       | int    | blue (0-255)  |
+
+**Returns** [`instance`](#Methods)
+
+### `fromRgba([r, g, b, a])`
+
+| parameter | type   | description   |
+| --------- | ------ | ------------- |
+| `r`       | int    | red (0-255)   |
+| `g`       | int    | green (0-255) |
+| `b`       | int    | blue (0-255)  |
+| `a`       | float  | alpha (0-1)   |
+
+**Returns** [`instance`](#Methods)
+
+### `fromHsl([h, s, l])`
+
+| parameter | type   | description        |
+| --------- | ------ | ------------------ |
+| `h`       | int    | hue (0-360)        |
+| `s`       | int    | saturation (0-100) |
+| `l`       | int    | luminosity (0-100) |
+
+**Returns** [`instance`](#Methods)
+
+### `fromHsla([h, s, l, a])`
+
+| parameter | type   | description        |
+| --------- | ------ | ------------------ |
+| `h`       | int    | hue (0-360)        |
+| `s`       | int    | saturation (0-100) |
+| `l`       | int    | luminosity (0-100) |
+| `a`       | float  | alpha (0-1)        |
+
+**Returns** [`instance`](#Methods)
+
+## Methods
+
+### `toRgbString()`
+
+**Returns** `rgb()` or `rgba()`, depending on the alpha.
+
+### `toHslString()`
+
+**Returns** `hsl()` or `hsla()`, depending on the alpha.
+
+### `toHexString()`
+
+**Returns** 6-digit or 8-digit `hex`, depending on the alpha.
+
+### `toRgbaArray()`
+
+**Returns** `[r, g, b, a]` array.