1.4.0

• Update to only check links prefixed by one of =", (, <, (a space).
• Linkie now finds all unique links at once, then uses multithreading to check them all.
• Linkie now rechecks links that had a ConnectionError, as these are often valid.
• Broken links in the SUMMARY are now also displayed with their status code.
• Dependency updates:
  • Update PyYaml from 4.2b4 to 5.1.1.
  • Update requests from 2.19.1 to 2.22.0.