Web Extensions Template has been superseded by Template
Use this template through the GitHub "Use this template" function, or:
set project=my-new-project
git clone --depth=1 https://github.com/lukesrw/template.git %project%
rmdir /S /Q %project%\.git
git init %project%
Once the Template has been cloned, you can type:
node tools/init extensions
This will download the Web Extensions blueprint files.