Add positional @Parameter annotation

[remkop]

This allows positional parameters to be assigned to separate fields with separate types.
usage example: <program> "header text" file1 23 file2 43

class Args {
  @Parameter(position=0, helpText="header text")       String headerText;
  @Parameter(position=1, helpText="binary input file") File binaryInput;
  @Parameter(position=2, helpText="record length")     int recordLength;
  @Parameter(position=3, helpText="text output file")  File output;
  @Parameter(position=4, helpText="max output lines")  int maxLines;
  ...
}

Definition:

@Parameter {
  int position;
  boolean required;
  String helpText;
  boolean hidden;
}

(Introduce a "positional parameters in progress" field?)