draft version of pub key aggregation

[n-hutton]

Hello,

Looking at the code, it disallows the flow of multiple actors signing and aggregating on the same message, presumably to avoid rogue public-key attacks.

However, this is a use case that is still useful if you first ensure all users prove they have the corresponding private key to their public key. This is what I would like to do. Do you have interest in me preparing this into a PR that would be accepted into this repo, or should I just work on my own fork? I would propose that the functionality to do this would be as a feature to prevent users accidentally using this.