Preallocate memory when deriving address from key

This makes src/address.AddrForKey preallocate 32 bytes before starting
the address derivation. As benches in syg_go show, reallocating temp
takes 20% of the function runtime.

src/address/address.go

@@ -64,7 +64,7 @@ func AddrForKey(publicKey ed25519.PublicKey) *Address {
 		buf[idx] = ^buf[idx]
 	}
 	var addr Address
-	var temp []byte
+	var temp = make([]byte, 0, 32)
 	done := false
 	ones := byte(0)
 	bits := byte(0)