The `new` method of loggers are now `#[must_use]`

[softdevca]

The new method of loggers are now #[must_use] to prevent confusion when new is used called instead of init.

Currently the following code will appear completely valid but silently not do any logging:

use log::*;
use simplelog::*;

fn main() {
    TermLogger::new(
        LevelFilter::Trace,
        Config::default(),
        TerminalMode::Stdout,
        ColorChoice::Auto,
    );
    error!("Red error");
    warn!("Yellow warning");
    info!("Blue info");
    debug!("Cyan debug");
    trace!("White trace");
}

With this change a compiler warning is generated on new.

[coveralls]

Coverage remained the same at 53.947% when pulling 80242aab3cd860e40208af4b2069d1b49a1be14a on softdevca:pr-must_use-new into 626467d20046edb9c020acfbae461c2dd9cb2e17 on Drakulix:master.

[Drakulix]

Thanks!