Merge "pdl: use docstrings instead of attribute arguments"

#[derive(Debug, StructOpt)]

#[structopt(name = "pdl-parser", about = "Packet Description Language parser tool.")]

struct Opt {

    #[structopt(short, long = "--version", help = "Print tool version and exit.")]

    /// Print tool version and exit.

    #[structopt(short, long = "--version")]

    version: bool,

    #[structopt(name = "FILE", help = "Input file.")]

    /// Input file.

    #[structopt(name = "FILE")]

    input_file: String,

}