Add basic CPack support

@ThijsWithaar is responsible for giving me the idea, but his PR
had couple of things that meant it was simpler to rewrite it than
to fix and merge it.

Supersedes and closes #1599

CMakeLists.txt

@@ -205,4 +205,15 @@ if (NOT_SUBPROJECT)
         ${PKGCONFIG_INSTALL_DIR}
     )
 
+    # CPack/CMake started taking the package version from project version 3.12
+    # So we need to set the version manually for older CMake versions
+    if(${CMAKE_VERSION} VERSION_LESS "3.12.0")
+        set(CPACK_PACKAGE_VERSION ${PROJECT_VERSION})
+    endif()
+
+    set(CPACK_PACKAGE_CONTACT "https://github.com/catchorg/Catch2/")
+
+
+    include( CPack )
+
 endif(NOT_SUBPROJECT)