Function crypto_crawler::crawl_l2_snapshot

pub fn crawl_l2_snapshot<'a>(
    exchange: &str, 
    market_type: MarketType, 
    symbols: &[String], 
    on_msg: Box<dyn FnMut(Message) + 'a>, 
    duration: Option<u64>
)

Crawl level2 orderbook snapshot through REST API.