SEP-10: muxed account and memo support

SEP-10 Muxed Account & Memo Support

SEP-10 now supports authenticating users of shared, pooled, or omnibus Stellar accounts.

These users are either represented using a muxed account (an M... address) or a Stellar account (G...) accompanied by an ID memo.

Allow muxed accounts as client account parameter values
Add a optional memo parameter that accepts a 64-bit integer representation and attach it to the challenge transaction returned
- If your language does not support optional parameters, this may be a breaking change
Disallow muxed client accounts and memos to be passed in the same call; they are mutually exclusive parameters

Allow muxed accounts as source accounts of the first operation within challenge transactions
Add a 64-bit integer representation memo to the return value if present in the challenge transaction
- Depending on the data type of the return value, this may be a breaking change
Disallow muxed client accounts and memos to be present in the challenge transaction; they are mutually exclusive

The JS and Python SDKs have implemented this functionality, please use them as references: