Fiscal Printer trait for implement

Allows define a trait using base values for documents send to and from fiscal printer.

Examples:

main.js

println!("Hello, world!");
    let epale_pnp: example::PnP = FiscalPrinter::new();
    epale_pnp.open_port(String::from("Epale"));
    epale_pnp.send_command(String::from("Ejele"));
    let setup = Setup::new(String::from("dsadadashdg-ajdhas"), String::from("lpt1"));
    let result = epale_pnp.setup(setup);
    println!("Result of Setup {:?}", result);
    epale_pnp.close_port();