Version 5.1.1 (TypeScript refactor)

The module has been converted to TypeScript and unit tests have been added. Internally, this means that it is easier and quicker to make future changes with confidence. Externally, it means that other TypeScript projects will be able to use kijiji-scraper with type checking. The new type definitions are also fully commented with TSDoc comments to serve as easily accessible documentation regardless of whether or not you are using TypeScript.