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**Added**:
- Added a new enum ``TimestampFormat`` for the ``timestamp()`` method.
**Updated**:
- The method ``timestamp()`` for ``Datetime()`` now expects one of the following timestamp formats: `TimestampFormat.POSIX`, `TimestampFormat.RFC_3339`, or `TimestampFormat.ISO_8601`.
- The ``datetime()`` method now has default parameters start and end set to the current year.
**Removed**:
- The method `timestamp()` no longer accepts the ``posix`` parameter.