Adds a TypeScript equivalent of the 'Get Started Using JavaScript'
tutorial, with runnable Node.js and Web code samples using xrpl.js.
From the issue it covers the TypeScript specific asks:
- Setting up a TypeScript project (typescript dep, tsconfig.json,
compile and run steps).
- Using xrpl.js's built-in types to build a transaction from input
values and validate it (typed Payment + xrpToDrops + validate()).
Closes#1208
