hash/fwd: add forward declerations

Makefile.am

@@ -107,6 +107,7 @@ UTIL_FILES   =			\
     guid.cpp			\
     guid.hpp			\
     hash.hpp			\
+    hash/fwd.hpp		\
     hash/simple.hpp		\
     hash/simple.cpp		\
     hash/adler.cpp		\

hash/fwd.hpp

@@ -0,0 +1,52 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2016, Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef __UTIL_HASH_FWD_HPP
+#define __UTIL_HASH_FWD_HPP
+
+// The single function call hashes are light weight enough to include
+// directly, and are unlikely to change given their inherent
+// lightweight nature.
+
+#include "./fasthash.hpp"
+#include "./fnv1a.hpp"
+#include "./murmur.hpp"
+
+
+// Forward declerations of class based hashes
+namespace util { namespace hash {
+    template <class T> class HMAC;
+
+    // checksums
+    class adler32;
+    class bsdsum;
+    class fletcher;
+    class crc32;
+
+    // hash adapters
+    class PBKDF1;
+    class PBKDF2;
+
+    // cryptographic hashes
+    class MD2;
+    class MD4;
+    class MD5;
+    class RIPEMD;
+    class SHA1;
+    class SHA256;
+} }
+
+#endif