Simpler Way To Crawl

At the moment, you can only 'crawl' through one block gaps by using trapdoors, which cause you to 'swim' through the gap. This is intentional but FEELS like a bug. I think it'd be much better where if you hold shift while moving against a one block gap, you'll start crawling through it. Adding a completely separate button just seems unnecessary, but this is probably the perfect balance.