add script to get the release notes

Usage:
```sh
npm run release-notes         # Gets notes for current version
npm run release-notes 1.2.3   # Gets notes for explicit version
```

package.json

@@ -14,7 +14,8 @@
     "build": "npm run swcify",
     "dev": "npm run swcify -- --watch",
     "postbuild": "tsc --emitDeclarationOnly",
-    "prepublishOnly": "npm run build"
+    "prepublishOnly": "npm run build",
+    "release-notes": "node ./scripts/release-notes.js"
   },
   "prettier": {
     "printWidth": 100,

scripts/release-notes.js

@@ -0,0 +1,16 @@
+let path = require('path')
+let fs = require('fs')
+
+let version = process.argv[2] || require('../package.json').version
+let changelog = fs.readFileSync(path.resolve(__dirname, '..', 'CHANGELOG.md'), 'utf8')
+let match = new RegExp(
+  `## \\[${version}\\] - (.*)\\n\\n([\\s\\S]*?)\\n(?:(?:##\\s)|(?:\\[))`,
+  'g'
+).exec(changelog)
+
+if (match) {
+  let [, date, notes] = match
+  console.log(notes.trim())
+} else {
+  console.log(`Placeholder release notes for version: v${version}`)
+}