Refactor to default to structured logging.

- Added `flattenMessage` and `FlattenedLogMessage` to default to
  structured logging.
- Rework the logic formatting messages for the ConsoleLogger.
- Add a more comprehensive README.

src/util.ts

@@ -0,0 +1,12 @@
+export function omit(
+  obj: Record<string, unknown>,
+  keys: string[],
+): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+  for (const key in obj) {
+    if (!keys.includes(key)) {
+      result[key] = obj[key];
+    }
+  }
+  return result;
+}