Generate and publish Sparkle appcasts
Generates appcasts for the following apps:
Appcasts are published to https://sparkle.jbmorley.co.uk.
Paths are of the form:
https://sparkle.jbmorley.co.uk/<owner>/<repo>/appcast.xml
e.g., The appcast for Thoughts is located at https://sparkle.jbmorley.co.uk/inseven/thoughts/appcast.xml.
Right now the list of apps is hardcoded in scripts/build.py. Adding an app is a matter of adding an entry to the repositories variable.