presskit.html 0.4.0

• More documentation. We need more.
• Fix gifs not being authorised.
• Add index.html to products' link by default, allowing a build to work even without a web server. To remove index.html links, build with the --pretty-links flag (which you should if you care about "The Beauty and the URL™").
• Add --clean-build-folder flag to delete the build folder before generating a new presskit.
• The --output flag allows the user to change the name of the build folder.
• Fix a bug with --output not creating folders recursively.
• Fix a bug with flexbox on IE.
• Publish an example at http://pixelnest.io/presskit.html/example/