Updated cmake export config

Followed the official cmake doc and added newest
export config.
https://cmake.org/cmake/help/latest/guide/tutorial/Adding%20Export%20Configuration.html

CMakeLists.txt

@@ -109,5 +109,26 @@ install(TARGETS iir_static EXPORT iir-targets
 install(EXPORT iir-targets
   DESTINATION lib/cmake/iir
   NAMESPACE iir::
-  FILE iir-config.cmake
+  FILE iirTargets.cmake
 )
+
+include(CMakePackageConfigHelpers)
+
+configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in
+  "${CMAKE_CURRENT_BINARY_DIR}/iirConfig.cmake"
+  INSTALL_DESTINATION "lib/cmake/iir"
+  NO_SET_AND_CHECK_MACRO
+  NO_CHECK_REQUIRED_COMPONENTS_MACRO
+  )
+
+write_basic_package_version_file(
+  "${CMAKE_CURRENT_BINARY_DIR}/iirConfigVersion.cmake"
+  VERSION "${iir_VERSION_MAJOR}.${iir_VERSION_MINOR}"
+  COMPATIBILITY AnyNewerVersion
+)
+
+install(FILES
+  ${CMAKE_CURRENT_BINARY_DIR}/iirConfig.cmake
+  ${CMAKE_CURRENT_BINARY_DIR}/iirConfigVersion.cmake
+  DESTINATION lib/cmake/iir
+  )

Config.cmake.in

@@ -0,0 +1,12 @@
+# Config.cmake.in
+
+@PACKAGE_INIT@
+
+# Value of 'iir_INCLUDE_DIRS' is real: it contains the include directory.
+set(iir_INCLUDE_DIRS @CMAKE_INSTALL_PREFIX@/include)
+
+# CMake extracts a library path from it.
+set(iir_LIBRARIES iir)
+
+# Include the export script generated by CMake:
+include(${CMAKE_CURRENT_LIST_DIR}/iirTargets.cmake)