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/batch.rs

@@ -1,3 +1,5 @@
+use std_shims::vec::Vec;
+
 use rand_core::{RngCore, CryptoRng};
 
 use zeroize::{Zeroize, Zeroizing};

crypto/multiexp/src/lib.rs

@@ -1,7 +1,12 @@
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 use core::ops::DerefMut;
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc;
+use std_shims::vec::Vec;
 
 use zeroize::Zeroize;
 

crypto/multiexp/src/straus.rs

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