C#/.NET console Windows app for website content change detection. Sends notifications to email via Mailgun HTTP API. It periodically opens all URLs in the list (in random order) and retrieves content (as text) using the specified selector. If the content changed since the last time, then it sends an email notification with a number of inserted/deleted lines and a DIFF text file. Also, it sends notifications about errors (if repeated more than once in a row) such as when the website is down...