Add ability to keep recurrence attributes on event copies

[Plonq]

Add an argument keep_recurrence_attributes to the of() function in order to manually undo the stripping of RRULE, RDATE, and EXDATE attributes from each event copy.

Changes

• Add argument to relevant functions
• Add tests
• Update readme

Why?

I agree with the reason these were stripped in the first place (#24). However, for my use case, I want to keep these attributes on each event so I can differentiate between normal events and recurring events. Without these attributes, all events look the same. For example, when displaying events to the user, I want to display the recurrence rules as well.

Alternative

An alternative would be to implement grouping. I.e, return events as a dict, grouped by the recurrence, or the source event they were created from (with a special group for non-recurring events). However I felt that was overly complicated and I went for the simpler solution.

[niccokunzmann]

@Plonq, this is very straight and orderly. Since I have not much time to manage this right now, I give you access to the repository and you can release a new version following the release process.
Thanks!

[Plonq]

@niccokunzmann

Thanks, I have released 0.2.0b (since this change was a feature not a bug I did minor version bump). I'm assuming the Pypi package will get updated automatically?

At first I thought 0.1.21b was never released, but later realised it was just the changelog and __version__ that hadn't
been updated. I fixed the changelog afterwards.

Also I noticed this message on Travis CI FYI: