docs(stats): correct attribute names and explain omitted zero counts Several examples used attributes that do not exist: unique_opens on the opens result, webmail, spam_complaints on the spam result, unique_clicks, browser_families, click_locations, and read_times/within_seconds. Use the real names, and show the dynamic-key results (email clients, browsers, read times) as the plain dicts they are. Explain that Postmark omits categories whose count is zero and that the SDK reports them as 0.
Initial Release