feat: automatically generate changelog after version bump

Fixes #23

package.json

@@ -9,6 +9,8 @@
     "documentation": "typedoc --includeDeclarations --excludeExternals --mode modules --out docs src",
     "install": "node lib/cli.js -p $INIT_CWD || true",
     "prepublishOnly": "npm ci && npm run build",
+    "postversion": "npm run changelog && git push && git push origin \"v$npm_package_version\"",
+    "preversion": "npm run prepublishOnly",
     "test": "echo \"Error: no test specified\" && exit 1",
     "tslint": "tslint -p tsconfig.json -c tslint.json 'src/**/*.ts'"
   },