CMakeLists.txt: replace hard coded install paths with use of GNUInsta…

…llDirs module, sets minimum required version of cmake to 2.8.5

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 2.8.5)
 project(inicpp)
 
 set(SRC_DIR src)
@@ -73,9 +73,10 @@ endif()
 
 
 # ========== Install targets - 'sudo make install' ==========
+include(GNUInstallDirs)
 include(InstallRequiredSystemLibraries)
-set(INCLUDE_INSTALL_DIR /usr/local/include CACHE PATH "Directory in which to install system header files.")
-set(LIB_INSTALL_DIR /usr/local/lib CACHE PATH "Directory in which to install system libraries.")
+set(INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_FULL_INCLUDEDIR} CACHE PATH "Directory in which to install system header files.")
+set(LIB_INSTALL_DIR ${CMAKE_INSTALL_FULL_LIBDIR} CACHE PATH "Directory in which to install system libraries.")
 if(UNIX)
 	install(DIRECTORY ${INCLUDE_DIR} DESTINATION ${INCLUDE_INSTALL_DIR})
 	install(TARGETS ${PROJECT_NAME} LIBRARY DESTINATION ${LIB_INSTALL_DIR} COMPONENT library)