Storage state checked before downloading.  Consolidated download code into helper method.
APK is downloaded to app-specific external storage directory.

Implemented in the form of a helper method to get the correct directory

Uses hardcoded storage path (/Android/data/<PACKAGE>/files) on API < 8
This has NOT been tested

Uses getExternalFilesDir() on API > 8
This has been tested on gingerbread

Also changed the filename to a constant.
Logged exceptions pass the Exception object to Log.? as well.
Updated changelog
jar file updated to latest version