Add deserialization for ICS

[jonasfranz]

This PR adds some basic deserialization features for parsing iCal-Files. The example implementation only contains a subset of the VEVENT element. This implementation could be extended in the future. I currently don't have time to implement the deserialization for all elements myself. Maybe somebody else can do it.

[lukas-h]

Thanks for the draft.

I planned to make the lib fully compliant with RFC 5545 #1

Will work on the parser soon

[emme1444]

@lukas-h any updates on this?

Would really like to have access to this for my app.

Thanks for the package so far!

[lukas-h]

Hi @emme1444 I didn’t put in the effort to build this feature. So we might ask @jonasfranz,
if we can get this PR ready to be merged.

[lukas-h]

As I see @jonasfranz, your branch is diverging from the dartclub/ical main.

Would be a great start to pull all of the new commits

Thanks for the effort!