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/src/consumer.js

@@ -0,0 +1,79 @@
+'use strict'
+
+const fs = require('fs')
+const bs = require('binary-search')
+const { promisify } = require('util')
+const readFile = promisify(fs.readFile)
+
+module.exports = class CharWidthTableConsumer {
+  constructor(data) {
+    this.data = data
+    this.emWidth = this.widthOf('m')
+  }
+
+  static create(data) {
+    return new CharWidthTableConsumer(data)
+  }
+
+  static async load(path) {
+    const json = await readFile(path)
+    const data = JSON.parse(json)
+    return new CharWidthTableConsumer(data)
+  }
+
+  static loadSync(path) {
+    const json = fs.readFileSync(path)
+    const data = JSON.parse(json)
+    return new CharWidthTableConsumer(data)
+  }
+
+  static isControlChar(charCode) {
+    return charCode <= 31 || charCode === 127
+  }
+
+  widthOfCharCode(charCode) {
+    if (this.constructor.isControlChar(charCode)) {
+      return 0.0
+    }
+
+    // https://github.com/darkskyapp/binary-search/pull/18
+    const index = bs(this.data, charCode, ([lower], needle) => lower - needle)
+    if (index >= 0) {
+      // The index matches the beginning of a range.
+      const [, , width] = this.data[index]
+      return width
+    } else {
+      // The index does not match the beginning of a range, which means it
+      // should be in the preceeding range A return value of `-x` means the
+      // needle would be at `x - 1`, and we want to check the element before
+      // that.
+      const candidateIndex = -index - 2
+      const [lower, upper, width] = this.data[candidateIndex]
+      if (charCode >= lower && charCode <= upper) {
+        return width
+      } else {
+        return undefined
+      }
+    }
+  }
+
+  widthOf(text, { guess = true } = {}) {
+    // Array.from() will split a string into an array of strings, each of
+    // which contains a single code point.
+    // https://stackoverflow.com/a/42596897/893113
+    return Array.from(text).reduce((accumWidth, char) => {
+      const charWidth = this.widthOfCharCode(char.codePointAt(0))
+      if (charWidth === undefined) {
+        if (guess) {
+          return accumWidth + this.emWidth
+        } else {
+          throw Error(
+            `No width available for character code ${char.codePointAt(0)}`
+          )
+        }
+      } else {
+        return accumWidth + charWidth
+      }
+    }, 0.0)
+  }
+}

node_modules/char-width-table-consumer/src/index.js

@@ -0,0 +1,16 @@
+'use strict'
+
+const CharWidthTableConsumer = require('./consumer')
+
+const {
+  create: createConsumer,
+  load: loadConsumer,
+  loadSync: loadConsumerSync,
+} = CharWidthTableConsumer
+
+module.exports = {
+  createConsumer,
+  loadConsumer,
+  loadConsumerSync,
+  CharWidthTableConsumer,
+}