• Support platforms that lack AtomicU64 support.

• Replace json with serde_json

• Add start_new to FlushGuard. You can now generate multiple traces in one run!
• Clean up dependencies
• Make events thread-scoped

Separate trace entries with newlines for easier viewing and manipulation (like with tail, etc).

• Add include_args option.
• Add name_fn and category_fn options.
• Improve event logging format.