provide a function while changing the month picker

[anubiju22]

As I am using this package and it's perfect for my flutter app design wise. So while loading a page with current date and month, an api call is working ng on onDateChange() function. But on changing the month, it remains the same as the api is already called. So it would be better to add a function while changing the month too.

[FadyFayezYounan]

Thank you for your feedback. I will provide this feature as soon as possible.