Project references

TypeScript 3 allows TypeScript projects to depend on other TypeScript projects by allowing tsconfig.json to reference other tsconfig.json files.

This makes it easier to split our code up into smaller projects. Our frontend code might be in TypeScript, in addition to having our backend in TypeScript. With TypeScript 3, we can have a frontend TypeScript project, a backend TypeScript project, and a shared TypeScript project that contains code that is used in both the frontend and backend. Splitting our code up into smaller projects can also can give us faster builds, because they can work incrementally.