Rexilion API docs

Rexilion API metric changelog

Added metrics, interval updates, public docs updates, and API contract corrections for Rexilion API.

Latest entries cover BTC transaction input/output means and output-to-input ratio metrics, 15-minute exchange premium gap and index support, API contract alignment, daily metrics, and options metrics.

• Rexilion API overview
• Authentication
• Errors
• Metric docs
• OpenAPI JSON