Simplify DOWNLOAD macro

Simplify DOWNLOAD macro

No need to spawn an extra sh.
Use short flags for curl and quote operands.
Replace sleep with read, let the user close the download window instead
of waiting for an arbitrary time.
Rename d to reflect what it's used for.
Reorder sh positional arguments.
Set $0 to a command name and shift other positional parameters to
clarify the "sh -c" command.