message: Appveyor: Set path for dronecore source dir
  It is confusing to use relative path like "cd ..\..\..\". Its better
  to use a preset path. This preset path variable is used for traversal.
diff: @@ -51,7 +51,8 @@ build_script:
  ) else (
  nmake /f Makefile.vc mode=static VC=15 MACHINE=x64 DEBUG=no
  )
  - - cd C:\dronecore
  + - set dronecore_dir=C:\dronecore
  + - cd %dronecore_dir%
  - md build
  - cd build
  - if "%configuration%"=="Debug" (
  @@ -71,6 +72,7 @@ build_script:
  - cd %boost_dir%
  - bootstrap.bat
  - b2 --with-system --with-date_time --j%cores% toolset=%msvcver% address-model=64 architecture=x86 link=static threading=multi runtime-link=shared --build-type=minimal stage --stagedir=stage/x64
  + - cd %dronecore_dir%
  - cd example\takeoff_land
  - md build
  - cd build
  @@ -80,7 +82,7 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  - cd example\fly_mission
  - md build
  - cd build
  @@ -90,7 +92,7 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  - cd example\offboard_velocity
  - md build
  - cd build
  @@ -100,7 +102,7 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  - cd example\transition_vtol_fixed_wing
  - md build
  - cd build
  @@ -110,7 +112,7 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  - cd example\follow_me
  - md build
  - cd build
  @@ -120,7 +122,7 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  - cd example\fly_qgc_mission
  - md build
  - cd build
  @@ -130,14 +132,14 @@ build_script:
  ) else (
  cmake --build . --config Release
  )
  - - cd ..\..\..
  + - cd %dronecore_dir%
  test: on
  # We need to manually copy the dlls for now, otherwise they are not found.
  test_script:
  - - cd C:\dronecore
  + - cd %dronecore_dir%
  - if "%configuration%"=="Debug" (
  copy build\third_party\gtest\googlemock\gtest\Debug\gtestd.dll build\Debug\ &&
  copy build\third_party\gtest\googlemock\gtest\Debug\gtest_maind.dll build\Debug\ &&
  