Moving to TypeScript

Since the library is now used not only by vanilla Node.js projects but also in TypeScript projects (e.g., https://github.com/petrbroz/vscode-forge-tools), the existing codebase has been ported to TypeScript.

In previous versions of this library, providing authentication data to Forge client classes was optional (the clients would pull the credentials from env. variables instead), but starting with version 2 the authentication data is required. This breaking change is introduced so that in future this library can be used in environments where process is not available, e.g., bundled for browsers.