main : allow a response-file as the sole parameter (#2019)

main : allow a response-file as the sole parameter (#2019)

* The "main" example now allows a response-file as the sole parameter.

A response-file is a text file with command-line parameters, one per line.
Prefix the name of the response-file with "@" to identify it as such.
It's used under MS Windows to work around command-line length limits.
It may be useful under other platforms to simplify character-escaping.

* minor : style

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Co-authored-by: Georgi Gerganov <redacted>