This function takes no parameters
You may encounter a situation where you'll need to know what the highest valid entry ID currently is. When this happens, you can use this method to retrieve it.
If this method fails for any reason, it returns -1. Otherwise, it returns the highest valid entry ID.
Note: while this is the most recent post by ID, the datestamps on posts can be altered. This means that it may not be the last post in chronological order. Use GetMostRecentEntry
instead if you want to find that post.