[vpicc] update Appveyor with better swig install

choco install of swig only give us the executable, not the libraries needed for package compilation

Best way is to direct download it from sourceforge, extract it to a folder and then add that folder to PATH env variable.

appveyor.yml

@@ -23,7 +23,10 @@ install:
  # BUGFIX: wdf directory was renamed to 00wdf, rename it back (see github.com/appveyor/ci/issues/414)
  #- ps: ren 'C:\Program Files (x86)\Windows Kits\10\include\00wdf' 'wdf'
 
- - choco install swig
+
+ - (new-object net.webclient).DownloadFile('https://sourceforge.net/projects/swig/', '..\swig.zip')
+ - Expand-Archive -LiteralPath ..\swig.zip -DestinationPath ..\swig_folder
+ - $env:Path += "..\swig_folder"
  - python -m pip install --upgrade pip
  - pip install virtualenv
  - pip install -U setuptools