android: create/clean a temporary directory on startup: directory returned by tempfiles on Android is actually the root directory of the application, so it is not cleaned. To work around that a `/tmp` directory inside it is now created, and cleaned on startup if it already exists.

-e git+https://github.com/kivy/kivy.git#egg=kivy
-e hg+https://repos.goffi.org/sat#egg=sat
-e .