Crawl sync option

1. ability to crawl links in sync.

fn main() {
   // crawl one by one 
    let mut website: Website = Website::new("https://choosealicense.com");
    website.crawl_sync();
}

or via the cli.

spider -d https://rsseau.fr crawl -s

What's Changed

• chore(log): add crate log default logger by @j-mendez in #42
• feat(delay): add non blocking delay scheduling by @j-mendez in #43

Full Changelog: v1.6.1...v1.7.3