Return IbcReceiveResponse (no Result wrapper) from `ibc_packet_receive`

[ethanfrey]

We really want to discourage returning errors - they should return success and an error acknowledgement. A few techniques are documented in IBC.md now since #885

To make this more explicit we can just prevent returning an error. This would be different than all other entry points, but maybe desirable. Open for feedback (do it or close issue).

[webmaster128]

On the other hand: if people start to use panics instead, it gets even worse then returning errors.

[ethanfrey]

I think the api interface should allow returning errors (you are right, panic is worse).

I did add some extensive documentation on both receiving packets and on error handing in receive

Maybe that is enough to close this issue?

I would be happy if some other devs read those docs and make a concrete issue if anything is missing there, which I can close by improving the docs.

[ethanfrey]

Writing an IBC contract is non-trivial and people will need to read docs to understand it. We cannot encode all this info in the type system.

I would also love to have a larger collection of IBC examples to demo...

[webmaster128]

Great, let's keep as is for consistency. Best practive will emerge for how to converts errors to acknowledgements.