Close file.
close-file closes file <file id> previously opened with
open-file, where <file id> is an open file identifier.
You can obtain the status of file closing via optional <status> (in
"status" clause), which can be created with optional
"define". The <status> is VV_OKAY if file is closed, or VV_ERR_CLOSE if could not close file.
If you do not close a file opened with open-file, Vely will automatically close it when the request ends.