1.8.0

Enhancements

• Invoker doesn't send request again on nack
• More descriptive handling of dropped ws connections
• Make cachex optional (only needed by action_handler)
• Explicit support of new action-api features:
• Log "hello" message when ws connection is successfully established
• Invoker sends "last call" instead of immediate timeout (maybe cached response is waiting but wasn't delivered)
• More descriptive timeout messages (with last success status in action api)
• CI tests for elixir >= 1.15