calendar 관련 자료

event 추가

https://stackoverflow.com/questions/17791178/android-calendarprovider-events-color

안드로이드 event column

https://developer.android.com/reference/android/provider/CalendarContract.EventsColumns

구글 operation example

https://github.com/codexpedia/android_google_calendar_crud/blob/master/app/src/main/java/com/example/googlecalendar/MainActivity.java

https://www.codexpedia.com/android/crud-operations-using-calendar-provider-in-android/