With

• Added httr_progress function to use the waitress or
  the attendant instead of httr::progress.
• Added withProgressWaitress, setProgressWaitress, and
  incProgressWairess analogous to the same functions in shiny.
• Added withProgressAttendant,
  incProgressAttendant, and setProgressAttendant.
• Fix major issue with Hostess, it was basically broken
  #108.
• Add withWaiter as requested in
  #105