feat: add TS type declarations

[ImRodry]

This PR adds built-in TS type definitions taken from https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/safe-regex (aka npmjs.com/package/@types/safe-regex)

Note for the future and for maintainability: these types only need to be changed if:

• A new export is added to the package (either a function, object, etc)
• A new parameter is added to the function
• A new option is added to the options interface

In order to update the options, simply add a new line after the existing one and type the name of the option followed by its type. You can see TS's most basic types here: https://www.w3schools.com/typescript/typescript_simple_types.php

If adding a new export that isn't the default export, simply declare it with the export keyword before it. Be sure to give it the same name it has in the code!

[ImRodry]

This PR supersedes #29 as it was outdated and had merge conflicts