message: made hello_world a part of appveyor test
diff: add_executable(hello_world hello_world.cc)
  target_link_libraries(hello_world PRIVATE DataFrame)
  hmdf_target_data_files(hello_world
  - DATA_FILES ${PROJECT_SOURCE_DIR}/data/SHORT_IBM.csv
  + DATA_FILES
  + ${PROJECT_SOURCE_DIR}/data/IBM.csv
  + ${PROJECT_SOURCE_DIR}/data/DT_IBM.csv
  + ${PROJECT_SOURCE_DIR}/data/DT_AAPL.csv
  )
  +add_test(NAME hello_world COMMAND hello_world)
  