Added interface target to config file for cmake versions > 3.0

Author: Walter Gray

websocketpp-config.cmake.in

@@ -6,3 +6,9 @@
 @PACKAGE_INIT@
 set_and_check(WEBSOCKETPP_INCLUDE_DIR "@PACKAGE_INSTALL_INCLUDE_DIR@")
 set(WEBSOCKETPP_FOUND TRUE)
+
+#This is a bit of a hack, but it works well. It also allows continued support of CMake 2.8
+if(${CMAKE_VERSION} VERSION_GREATER 3.0.0 OR ${CMAKE_VERSION} VERSION_EQUAL 3.0.0)
+  add_library(websocketpp::websocketpp INTERFACE IMPORTED)
+  set_target_properties(websocketpp::websocketpp PROPERTIES INTERFACE_INCLUDE_DIRECTORIES "${WEBSOCKETPP_INCLUDE_DIR}")
+endif()