Middleware Processing for IA

[lucasjhall]

Added

• process_request_options() from Munki
• Middleware section in Readme

Changed

• downloadfile(options) and download_if_needed(item) now attempt to process through middleware
• markdown formatting in Readme

[erikng]

sorry for never merging this. Should I close this now given your current status or is this something that's still good to go/needed?