Added basic TypeScript typings

[JohnWeisz]

This PR adds index.d.ts containing typings, but without descriptions (as of now). This allows codec-parser to be used in TypeScript projects nicely.

There are no changes to runtime code, these are merely declarations for IntelliSense, etc. to work better.

[CharlesSchimmel]

Could you also update format in package.json to include formatting TypeScript files, and then run npm format and push the changes? Just add --write **/*.ts to this line.

[CharlesSchimmel]

This is so helpful, thanks for doing this!

[CharlesSchimmel]

I think this can be narrowed to (string: codec) => {}. @eshaz onCodec is called with a string that is the name of the codec being used, and is expected to be an arbitrary action?

[eshaz]

I think it a union could be used here that is dependent on the passed in mimetype on instantiation.

• When the mimetype is like aac or mpeg, then onCodec will be called with aac and mpeg respectively.
• When the mimetype is like ogg, then onCodec may be called with one of flac, opus, or vorbis depending on the detected codec.

See: https://github.com/eshaz/codec-parser/search?q=onCodec and https://github.com/eshaz/codec-parser#properties

This is something I can add myself later too.

[JohnWeisz]

For now I added an enum to constrain codec to the possible codec strings.

[CharlesSchimmel]

Could these also be broken out into individual type aliases for each string?

[eshaz]

Thanks @JohnWeisz for your contribution! I've been meaning to add types but you beat me to it :) Feel free to make updates based on the comments here if you want. Otherwise, I'll merge this into a branch and take care of the modifications.

[JohnWeisz]

Thanks, I pushed a few more changes, in particular to get formatting done and flesh out the onCodec callbacks.

Also I realized that, because of the type: "module" in package.json, we need to make the type declaration itself a module, so I also converted that to top-level module exports.

Note: I ran prettier locally and it essentially affected every .js file in the repo. I didn't push those.