Added NPM build script

.gitignore

@@ -0,0 +1 @@
+npm

_npm.ts

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+/**
+ * This script builds the NPM package from Deno source
+ */
+import { build, emptyDir } from "https://deno.land/x/dnt@0.35.0/mod.ts";
+
+await emptyDir("./npm");
+
+await build({
+  entryPoints: ["./mod.ts"],
+  outDir: "./npm",
+  shims: {
+    // see JS docs for overview and more options
+    deno: true,
+    undici: true,
+    crypto: true,
+  },
+  package: {
+    // package.json properties
+    name: "workflowy",
+    version: Deno.args[0],
+    description: "WorkFlowy client for reading and updating of lists",
+    author: "Karel Klima <karelklima@gmail.com> (https://karelklima.com)",
+    license: "MIT",
+    repository: {
+      type: "git",
+      url: "git+https://github.com/karelklima/workflowy.git",
+    },
+    bugs: {
+      url: "https://github.com/karelklima/workflowy/issues",
+    },
+    mappings: {
+      "https://deno.land/x/zod@v3.21.4/mod.ts": {
+        package: "zod",
+        version: "^3.21.4",
+      },
+    },
+  },
+  postBuild() {
+    // steps to run after building and before running the tests
+    Deno.copyFileSync("LICENSE", "npm/LICENSE");
+    Deno.copyFileSync("README.md", "npm/README.md");
+  },
+});