Exposing init_logger to the public API for uniform logging across preprocessors

[jeertmans]

Problem

Currently, all preprocessors need to call their own logging library. As calls to preprocessors are done within the main mdBook process, it would make sense to have a uniform logger across all preprocessors, so that when they log messages, it does not look weird compared to mdBook's own logging.

Proposed Solution

Move main::init_logger to utils::init_logger and make it public, so that people can opt in for the same logger as mdBook.

mdBook/src/main.rs

Lines 97 to 121 in efb671a

	fn init_logger() {
	let mut builder = Builder::new();
	builder.format(|formatter, record| {
	writeln!(
	formatter,
	"{} [{}] ({}): {}",
	Local::now().format("%Y-%m-%d %H:%M:%S"),
	record.level(),
	record.target(),
	record.args()
	)
	});
	if let Ok(var) = env::var("RUST_LOG") {
	builder.parse_filters(&var);
	} else {
	// if no RUST_LOG provided, default to logging at the Info level
	builder.filter(None, LevelFilter::Info);
	// Filter extraneous html5ever not-implemented messages
	builder.filter(Some("html5ever"), LevelFilter::Error);
	}
	builder.init();
	}

Notes

No response