Reorganized modules, made rules a separate struct

Rules are now a separate struct, and the `rules` member of
`settings::Settings` is now a `Vec<settings::rule::Rule`.

Several elements were made private, now can be accessed through
dedicated methods

src/lib.rs

@@ -19,6 +19,7 @@ use log::{info, warn};
 use simplelog::*;
 
 pub mod settings;
+mod utils;
 
 /// Initializes the crate
 ///