Issue Description

Type: feature request

Describe what happened (or what feature you want)

Implement Sentinel in Rust, including basic statistic and flow control functionalities. Some expected features:

• Basic statistic structure (sliding window that can achieve high concurrency and accuracy)
• Rate limiting (based on sliding window, token bucket or leaky bucket algorithm)
• Circuit breaking
• Metrics interface that can pump real-time metrics to outside consumer
• Embedded API server (HTTP-based)

Discussions and contributions are welcomed!