hub 2.8.4

• Add hub api -H flag to set HTTP request headers

• Add hub api -i flag to output HTTP response headers

• Change how hub api deals with HTTP errors:

  • HTTP response is now printed on stdout regardless of HTTP status
  • No longer print an extra newline after HTTP response body
  • No more Error: HTTP {STATUS} message on stderr
  • hub exits with status 22 instead of 1

• Fix hub execution under WSL (Windows Subsystem for Linux)