to create .ics “event files”, as described in RFC 5545 https://tools.ietf.org/html/rfc5545
• Version (3.7.4)
• Classification (3.8.1.3)
• Location (3.8.1.7)
• Priority (3.8.1.9)
• Summary (3.8.1.12)
• DTSTART (3.8.2.4)
• DTEND (3.8.2.2)
• Time zone identifier (3.8.3.1)
• Sent-by (3.2.18)
• Resources (3.8.1.10)
• Geographic Position (3.8.1.6)
• Aspects of Recurring Events (3.8.5)
• RSVP (3.2.17)
https://github.com/eligrey/FileSaver.js/
https://stackoverflow.com/questions/21997057/how-to-use-filesaver-js
https://github.com/TeamRambutan/Calendar
https://www.w3resource.com/javascript/form/all-letters-field.php
https://stackoverflow.com/questions/46155/how-to-validate-an-email-address-in-javascript
https://stackoverflow.com/questions/44956890/regex-how-to-prevent-repeated-special-characters