Add possibility to expand weekly recurring event starting from the specified start date

[stsiarzhanau]

Hi! Thanks for the handy lib)

There could be the case when we create a recurring event and set it to repeat for example on Thursdays, but specify Monday as start date.
Generally in this case event occurrencies will be created starting from the first Thursday that occurs after specified start date.
On Monday event occurrence will not be created.
This is the way how Google Calendar expands events. The same does ical-expander.

But some calendars (like the one in Kerio Connect app) behave differently: the first occurrence is created for the specified start date (Monday) and all other on Thursdays.

On my current project customer wants the behavior to match the one in Kerio Connect.

Could you please provide some thoughts how it can be implemented in the right way?

Also, it'd be great if you add some option to the lib, that will allow to achieve this behavior.

[mifi]

I don't have the time to implement this now but if it can be implemented in a simple way, a PR is welcome