v0.7.4

Highlights

• add a new 30s timeout for fetching web page content for the crawler
  • the async reqwest::get function by default does not have a timeout and thus we could potentially stuck waiting
    forever.
• add new max_delay_secs parameter to the /health endpoint to allow user specify a maximum delay in seconds and
  the API will return error code 503 if the delay for the latest file timestamp (any file) is greater than the specified
  value.
  • this allows better monitoring for the API's health without sending heartbeats.