Change package name to du-dust

The binary is still called dust. Sadly dust was taken on crates.io.
This change should allow us to send this crate to crates.io

src/main.rs

@@ -1,14 +1,15 @@
 #[macro_use]
 extern crate clap;
 extern crate assert_cli;
-extern crate dust;
 
 use self::display::draw_it;
 use clap::{App, AppSettings, Arg};
 use utils::{find_big_ones, get_dir_tree};
 
+
 mod display;
 mod utils;
+mod lib;
 
 static DEFAULT_NUMBER_OF_LINES: &'static str = "15";