Use universal reference instead of paying std::function overhead

Author: rigtorp

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -308,7 +308,7 @@ private static void generateGroupClassHeader(
  indent + " }\n" +
  indent + " }\n\n" +
  indent + "#else\n" +
- indent + " inline void forEach(std::function<void(%1$s&)> func)\n" +
+ indent + " template<class Func> inline void forEach(Func&& func)\n" +
  indent + " {\n" +
  indent + " while(hasNext())\n" +
  indent + " {\n" +
@@ -840,7 +840,6 @@ private static CharSequence generateFileHeader(
  "#endif\n\n" +
  "#if __cplusplus >= 201103L\n" +
  "# include <cstdint>\n" +
- "# include <functional>\n" +
  "# include <string>\n" +
  "# include <cstring>\n" +
  "#endif\n\n" +