New "browse" UI

Also, separated out browse, ?meta, and ?module request handlers.

Fixes #82

modules/utils/markup.js

@@ -0,0 +1,13 @@
+import { createElement } from 'react';
+
+export { createElement };
+
+export function createHTML(code) {
+  return { __html: code };
+}
+
+export function createScript(script) {
+  return createElement('script', {
+    dangerouslySetInnerHTML: createHTML(script)
+  });
+}