Downloader

If you ask for the cacheTag before calling download(), you will get the same one you passed in (if any). If you call it after download(), you will get the new cacheTag from the server, or null if there was none.

Cancel a running download, triggering an InterruptedException

Call this to start the download. Never call this more than once. Create a new Downloader, if you need to download again!

After calling download, this returns true if a new file was downloaded and false if the file on the server has not changed and thus was not downloaded.