Renamed isLessThan() / isGreaterThan() methods with isAfter() / isBefore()

Removed ...OrEqualTo() methods, as they are not strictly necessary.
Replaced LocalDateRange iterator with a generator
Removed LocalDate::toInteger(), changed MIN_DATE and MAX_DATE

toInteger() is redundant with toEpochDay(), and has no specific use case.
MIN_YEAR and MAX_YEAR have been lowered to (-) 999,999 to avoid 32-bit integer overflow in toEpochDay().