No longer use the log crate in light-base

[tomaka]

Instead, the PlatformRef trait should get a log function.

[tomaka]

Most likely API:

    fn log<'a>(
        &'a self,
        log_level: LogLevel,
        target: &str,
        text: &str,
        parameters: &mut dyn Iterator<Item = (&'a str, fmt::Arguments<'a>)>,
    );

The only problem is it's not clear to me how the default platform should behave. I suppose that it should use the log crate?