Add no_std support to transcript, dalek-ff-group, ed448, ciphersuite, multiexp, schnorr, and monero-generators

transcript, dalek-ff-group, ed449, and ciphersuite are all usable with no_std
alone. The rest additionally require alloc.

Part of #279.

crypto/multiexp/src/straus.rs

@@ -1,3 +1,5 @@
+use std_shims::vec::Vec;
+
 use zeroize::Zeroize;
 
 use ff::PrimeFieldBits;