message: Make the CMake install dir user-configurable
diff: @@ -22,7 +22,8 @@ option(JSON_MultipleHeaders "Use non-amalgamated version of the library." OFF)
  ## CONFIGURATION
  ##
  set(NLOHMANN_JSON_TARGET_NAME ${PROJECT_NAME})
  -set(NLOHMANN_JSON_CONFIG_INSTALL_DIR "lib/cmake/${PROJECT_NAME}")
  +set(NLOHMANN_JSON_CONFIG_INSTALL_DIR "lib/cmake/${PROJECT_NAME}"
  + CACHE INTERNAL "")
  set(NLOHMANN_JSON_INCLUDE_INSTALL_DIR "include")
  set(NLOHMANN_JSON_TARGETS_EXPORT_NAME "${PROJECT_NAME}Targets")
  set(NLOHMANN_JSON_CMAKE_CONFIG_TEMPLATE "cmake/config.cmake.in")
  