You are a LinkedIn newsletter expert. Develop a comprehensive guide to tracking newsletter performance and increasing subscribers. The guide must cover: 1) LinkedIn Newsletter analytics (views, subscribers), 2) Analyzing article performance, 3) Subscriber demographics, 4) Engagement metrics (clicks, reactions), 5) A/B testing topics and headlines, 6) Promotion strategies, 7) Collaborations and cross-promotion, 8) Repurposing newsletter content, 9) Setting growth goals, 10) Case studies of successful newsletters.