Possibly a bug: Add public access control to AES.Error and ChaCha20.Error

Fixing the below errors which occurs when try to catch error
out side of CryptoSwift module:
Type 'AES' has no member 'Error'
Type 'ChaCha20' has no member 'Error'

CryptoSwift/AES.swift

@@ -8,7 +8,7 @@
 
 final public class AES {
     
-    enum Error: ErrorType {
+    public enum Error: ErrorType {
         case BlockSizeExceeded
         case InvalidKeyOrInitializationVector
         case InvalidInitializationVector

CryptoSwift/ChaCha20.swift

@@ -8,7 +8,7 @@
 
 final public class ChaCha20 {
     
-    enum Error: ErrorType {
+    public enum Error: ErrorType {
         case MissingContext
     }