Pass headers through on HttpException class

[baileywickham]

For handling rate limits, I'd like to use the headers referenced here. To do this, an HTTPException needs to pass have the http headers of a response as an attribute. I'm happy to implement this, let me know if this is something you'd accept a PR on.

[baileywickham]

Ah, after looking further into it, it looks like the response object is a child of the cause of the error in the case where the error is an Axios error. One improvement would be typing that or providing handlers but the data is there. Feel free to close this issue if you consider it closed.