Add a bytes32[] parameter in swap()

[yisiliu]

I am thinking about if it's a good idea to add bytes32[] data to swap() to add more expressiveness, e.g. a merkle-proof based whitelist. The reason why I haven't added it to our contract is that, all the merkle proofs need to be stored somewhere other than a blockchain since it's way too expensive and useless to do so.

However, if we store them in a third-party storage, we are taking the risk of an unstable connection to that endpoint(e.g. AWS S3), causing some of our users not to be able to get the proof to participate in the ITO in time. What do you think what we should do here?

I can definitely add it here but I am afraid it'll add too much complexity to the whole process towards an unstable state for our users.