[C++]: move sbe.hhp to sbe.h.

Author: tmontgomery

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

@@ -803,7 +803,7 @@ private CharSequence generateFileHeader(final String namespaceName, final String
  "# include <functional>\n" +
  "# include <string>\n" +
  "#endif\n\n" +
- "#include <sbe/sbe.hpp>\n\n",
+ "#include <sbe/sbe.h>\n\n",
  namespaceName.toUpperCase(),
  className.toUpperCase()
  ));