Adds a script for running the test suite on Android emulator devices. Starting
with a fresh install of the Android Commandline tools; the script manages
installing other requirements, starting the emulator (if required), and
retrieving results from that emulator.
Add code and config for a minimal Android app, and instructions to build and run it.
Improve Android build instructions in general.
Add a tool subcommand to download the Gradle wrapper (with its binary blob). Android
studio must be downloaded manually (due to the license).
