Support X-WR-CALNAME and other properties

[bertiewils]

Is your feature request related to a problem? Please describe.
This might already be covered by #65, in which case feel free to close as a dupe.

The iCalendar spec supports a lot of extra properties (https://en.wikipedia.org/wiki/ICalendar#Extensions), but the common ones that are used are:

X-WR-CALNAME
X-WR-CALDESC
X-WR-TIMEZONE
X-PUBLISHED-TTL

They're used by some clients to pre-fill the calendar name, description etc when adding or subscribing to a calendar.

There's also rfc7986 that proposes NAME, DESCRIPTION etc properties, but that hasn't got very far.

Example;

$ curl -s https://calendar.google.com/calendar/ical/en.uk%23holiday%40group.v.calendar.google.com/public/basic.ics | head
BEGIN:VCALENDAR
PRODID:-//Google Inc//Google Calendar 70.9054//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-WR-CALNAME:Holidays in United Kingdom
X-WR-TIMEZONE:UTC
X-WR-CALDESC:Holidays and Observances in United Kingdom
BEGIN:VEVENT
DTSTART;VALUE=DATE:20211227

Describe the solution you'd like
The ability to add at least the following extra properties, or any custom values, when creating a calendar.

X-WR-CALNAME
X-WR-CALDESC
X-WR-TIMEZONE

FWIW here's how ics-py handles it simonw/datasette-ics#4 (comment)

[allenporter]

Hi thanks for the request. How are you expecting support for this to look like? E.g. how do you expect these properties to be exposed?

[bertiewils]

Thank you for your work on the package!

I'm not exactly sure, to be honest.

My use case is purely writing ics files, so maybe something similar to calendar.events.append(). e.g.

calendar = Calendar()
calendar.properties.append(name="X-WR-CALNAME", value="Calendar name")

which then gets added to the IcsCalendarStream before the events.

I'm not familiar with the reading/parsing side so can't be of much help I'm afraid.