Add TypeScript typings and small documentation changes

[101arrowz]

No functional changes were made; I only corrected some documentation and added TypeScript typings. This should allow TypeScript users to have compiler warnings when they input invalid data into functions, and should also allow JavaScript users with certain code editors (such as VSCode) to get better autocomplete.

[CLAassistant]

All committers have signed the CLA.

[101arrowz]

@JakeChampion Have you had time to review this yet?

[JakeChampion]

Hi @101arrowz, thanks for taking time to make this pull-request. This project does not use TypeScript and we ship JSDoc comments as our type documentation. I won't be accepting pull-request which as TypeScript types. Our other polyfill project has it's TypeScript types in the DefinitelyTyped @types project, I would recommend adding your types to the DefinitelyTyped project as well :-)

[101arrowz]

Alright, I'll submit the types to DefinitelyTyped. I'd like to ask that you consider updating at least the listAliases JSDoc, which suggests it returns an Array when it really returns an object. Thanks for the quick response!