Pmtiles js v4 (#499)

* pmtiles js v4: remove pmtiles spec v2 compatibility [#287]
* restructure ts files into src
* add tsup for building ESM/CJS and making types work in ESM
* bump fflate dependency
* update CHANGELOG for js 4.0.0

js/tsup.config.ts

@@ -0,0 +1,42 @@
+import { defineConfig, type Options } from "tsup";
+
+const baseOptions: Options = {
+  clean: true,
+  minify: true,
+  skipNodeModulesBundle: true,
+  sourcemap: true,
+  target: "es6",
+  tsconfig: "./tsconfig.json",
+  keepNames: true,
+  cjsInterop: true,
+  splitting: true,
+};
+
+export default [
+  defineConfig({
+    ...baseOptions,
+    entry: ["src/index.ts"],
+    outDir: "dist/cjs",
+    format: "cjs",
+    dts: true,
+  }),
+  defineConfig({
+    ...baseOptions,
+    entry: ["src/index.ts"],
+    outDir: "dist/esm",
+    format: "esm",
+    dts: true,
+  }),
+  defineConfig({
+    ...baseOptions,
+    outDir: "dist",
+    format: "iife",
+    globalName: "pmtiles",
+    entry: {
+      "pmtiles": "src/index.ts",
+    },
+    outExtension: () => {
+      return { js: ".js" };
+    },
+  }),
+];