This makes it work well in VS Code (f.e. it will use $ts-watch mode to read errors from stdout and display them in the "PROBLEMS" pane).
Plus this tells newcomers how to quickly get things started in dev mode (watch mode) for easy dev cycles.
Brings back default exports for backwards compatibility, but this time in a way that works with AMD and CJS module formats without build tool hacks. Uses rollup-plugin-dts to generate the type declaration for the bundle output, removing the brittle regex-based wrangling we were doing.
