- In preparation for some new features, some public APIs have been changed:

- High-level APIs that read input files from the file system (`transpileFiles` and `transpileProject`) now write transpiled files by default. This behavior can be changed by providing a `writeFile` callback, similarly to TypeScript's `program.emit`.

- `transpile` and `emitTranspiledFiles` functions have been replaced with the `Transpiler` class. See [documentation](https://typescripttolua.github.io/docs/api/overview#low-level-api) for usage examples.

- Fixed `declarationDir` option not being respected.

- `Function.length` is supported now.

- String iteration is now supported.

- Exposed `parseConfigFileWithSystem` to parse _tsconfig.json_ files as part of the tstl API.

- Fixed several other string operations behaving differently from JS (mostly regarding indices out of bounds and NaN arguments).

- Fixed a bug where the length argument of `String.prototype.substr` was evaluated twice.

- Fixed some missing dependencies in LuaLib classes (Map, Set, WeakMap, WeakSet)