Integrate TypeScript - Githubissues

Integrate TypeScript using babel @babel/typescript
Update ESLint config to support TypeScript files (using @typescript-eslint/eslint-plugin and @typescript-eslint/parser)
Set up build process using babel-cli, copyfile, rimraf and npm-run-all
Emit type definitions
Build before running tests so that CLI can be tested
Leave many TODOs to be resolved during further refactoring

Resolves #99

danvk / source-map-explorer