Add option to hold process until download is complete

[danemacmillan]

Right now when a file is selected for download using icd [filename], the process' control is immediately returned to the terminal, while the download continues asynchronously in the background. It would be nice to be able to pass an option that will essentially hold the process until the download is complete.

This would provide some nice scripting potential. For example, I have a modified cat function that does a few extra things depending on the file extension, so if I detect an *.icloud file, I can ensure that icd is called on it first, wait until the download is complete, then cat out the contents.

[farnots]

https://developer.apple.com/documentation/foundation/nsnotification/name/1407629-nsubiquityidentitydidchange