like the rest of processing, we want the android tools to be automatically
installed and available. no setting up environment variables for
ANDROID_SDK and PATH.

this may be a matter of auto-download of the tools via repository.xml, or
simply bundling them with the download.

however, to install the 1.6 and 2.0 platforms along with the SDK, the
result is a ~260 MB zip file, so it's not as simple as making a separate
android tool download with everything.