It’s one thing to be a frustrated Google+ user. It’s another thing to be a frustrated user who happened to write an entire book on how to properly navigate and use Google’s social network. Kevin Purdy, the author of Google+: The Missing Manual, took to Twitter on Thursday to rant about how he had no idea how to stop total strangers from sending him invitations to events that he had no interest in attending. “I am literally the author of a book on Google+, but cannot stop invites to SEO Hangouts in Cardiff, or St. Louis Tech Talks,’ ” Purdy fumed. “G+ has settings for ‘who can send notifications,’ ‘Who can Hangout with you,’ ‘Receive notifications-Events,’ and ‘Manage Subscriptions’… None of