Preprocessor: cleaned up an unnecessary header include

enum classes can be forward-declared. Also removed redundant version.hpp include
and did some include re-ordering.

src/serialization/preprocessor.cpp

@@ -22,17 +22,16 @@
 
 #include "buffered_istream.hpp"
 #include "config.hpp"
+#include "deprecation.hpp"
 #include "filesystem.hpp"
 #include "log.hpp"
 #include "serialization/binary_or_text.hpp"
 #include "serialization/parser.hpp"
 #include "serialization/string_utils.hpp"
-#include "version.hpp"
 #include "wesconfig.h"
-#include "deprecation.hpp"
 
-#include <stdexcept>
 #include <deque>
+#include <stdexcept>
 
 static lg::log_domain log_preprocessor("preprocessor");
 #define ERR_PREPROC LOG_STREAM(err, log_preprocessor)

src/serialization/preprocessor.hpp

@@ -17,19 +17,21 @@
 
 #pragma once
 
+#include "exceptions.hpp"
 #include "filesystem.hpp"
+#include "version.hpp"
+
+#include <boost/optional.hpp>
+
 #include <iosfwd>
 #include <map>
 #include <vector>
-#include <boost/optional.hpp>
-
-#include "exceptions.hpp"
-#include "version.hpp"
-#include "deprecation.hpp"
 
 class config_writer;
 class config;
 
+enum class DEP_LEVEL;
+
 typedef std::map<std::string, struct preproc_define> preproc_map;
 
 struct preproc_define