Added digest option to AppnetLogger.

I prefer my individual App.net posts to be individual entries in my Day One. If and only if you set the appnet_digest option to false (default is true), then these modifications will parse the new posts into individual Day One entries each timestamped with the time the App.net entry was posted. Otherwise, if appnet_digest is true the plugin will run as it did before.
Merge pull request #187 from scrooks/appnetdigest

Added digest option to AppnetLogger.