Background version checking; External storage behaviour;

[Kiirani]

Hi there, I had some trouble with the way your library was blocking to download the version file. I've modified it to use an asynctask to check the version and to extend observable to notify the application when this action is finished. Because this breaks compatibility with API 2, I've bumped version in my code to 2.1

There's a quick integration howto here: https://github.com/Kiirani/AppaholicsUpdateChecker/wiki/API-2.1-Integration-Guide

Update 19/04: Made some changes to download code so that it checks whether external storage will be available before downloading Downloads APK to the correct per-app location rather than to the root of the SD card Some changes to logging Bumped version to 2.2