Add --zero-terminated as long option

Cargo.toml

 [package]
 name = "hashtoc"
-version = "0.1.1"
+version = "0.1.2"
 authors = ["Anders Blomdell <anders.blomdell@control.lth.se>"]
 build = "build.rs"
 links = "libhash.a,libssl"

src/main.rs

@@ -604,6 +604,7 @@ fn main() {
              .help("Sets the level of verbosity"))
         .arg(Arg::with_name("zero-terminated")
              .short("z")
+             .long("zero-terminated")
              .help("End lines with NULL character"))
         .arg(Arg::with_name("max_age")
              .short("m")