Add -f flag for specifying that the last arguments are a list of filenames

[xyproto]

It is tradition for UNIX utilities to be able to specify one or more filenames as the last argument(s). By default, setconf does not support this, since setconf key=value filename is more readable.

This feature request is for adding a flag (perhaps -f, or -l) which means that the filename(s) comes last.