[Cryptography] Schnorr multisignatures based on ED22519

[jamesd at echeque.com]

I have heard it said that ED25519 supports Schnorr multisignatures,

The Libsodium documentation contains no mention of multi signatures, 
and, because ED25519 is nonprime group, it seems to me that implementing 
Schnorr multisignatures would require an expert in the mathematics of 
elliptic curves - I certainly have no idea how to even begin, and would 
not trust code written by someone not well known.

Libsodium supports the prime group Ristretto255, though only in the 
development version, not yet the stable version, with which a person of 
ordinary skills could implement Schnorr multisignatures but it is not 
apparent that this would play nice with LibSodium's built in high level 
encryption and signing code.

So, should I forget about Schnorr multisignatures, and just do what 
everyone else does:  Tuples?

Or does Libsodium support multisignatures somewhere in the 
documentation, and I have been looking in the wrong place?