Writing a Simple Blockchain

This section borrows code from [Savjee](https://www.savjee.be/2017/07/Writing-tiny-blockchain-in-JavaScript/), [Xavier Decuyper](https://www.codementor.io/@savjee/how-to-build-a-blockchain-with-javascript-part-1-k7d373dtk), and [Alibaba Cloud](https://www.alibabacloud.com/blog/build-your-own-blockchain-with-javascript_595314). Thank you for the inspiration!