Add getters for calendar and event properties

[qwandor]

Being able to parse an iCalendar file into a Calendar isn't much use if you can't then access the data in it in a useful way.

This PR adds typed getters to Calendar, Event, Todo, Venue and the Component trait, to get the same properties as the builder methods allow to be set.

I also:

• Derived some more basic traits (Clone, PartialEq, Eq) on some of the types that were missing them (Parameter, Property, Class, ValueType, EventStatus, TodoStatus).
• Added a getter on Property for the ValueType, and for the map of parameters.
• Allow a due date (without a time) to be specified for a TODO, as allowed by the RFC.

[hoodie]

Thanks for the work, you're right, this is very much needed. I actually was thinking about this already. Currently the Component objects are only builders, because that is how the library started. I didn't want to riddle the scope with get_ functions though, that's why I started adding a query() method that would return a corresponding type with all the getters (without the get_ prefix. Unfortunately I got interrupted.

Have a look here here perhaps https://github.com/hoodie/icalendar-rs/commit/27231259fe898f3a4495d0f6bc3e7659c748d8d1

What do you think?

[qwandor]

That commit doesn't include the ComponentQuery type so it's hard to say, but it seems a bit back to front and more complicated than necessary. Personally I prefer not to add separate types for builders versus data objects in Rust, but if you do want to I think it would make more sense to have the done method on the builder return the data object, which is then used everywhere else (including being the result of parsing a file). Or indeed you could have From implementations to convert back and forth between builder and data object. This would be an API breaking change though.

My preference, which would also be a breaking change but more idiomatic I think, would be to keep the current set of types, but rename the setters to set_ and have no prefix for the getters.

[qwandor]

I've separated the traits part into #38 so we can get that in at least, but I'd still like to get some solution to the problem of accessing calendar data in soon as I want to use this in something I'm working on for parsing iCalendar files as well as generating them.

[hoodie]

actually this looks pretty good. Thanks for the contribution. I would like to preserve conventional commit messages here, so I would go ahead and just add the prefixes to your commits. unless you would like to do that yourself

[qwandor]

Done.

[hoodie]

Thanks for the changes, I just released this as 0.12.0

[qwandor]

Thanks!