Xerparser

* Added `default_calendar` attribute to `PROJECT` class.

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Added

* Added `SCHEDOPTIONS` class.
* Added `options` attribute the `PROJECT` class, which is a `SCHEDOPTIONS` object.`
* Added `lineage` and `full_code` properties to the `ACTVCODE` class. [Issue 2](https://github.com/jjCode01/xerparser/issues/2)

Changes

* Comparison operators for `ACTVCODE` are now based on `full_code` property rather than `code` property.

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General Notes

Added some additional features noted below, and continue working on `Warnings` class.

Added

* Added `lineage` property to `PROJWBS` class. Returns list of all ancestor `PROJWBS` objects, including self.
* Added `duration` property to `TASK` class. This will return `remaining_duration` if the task is not started; otherwise, it returns `original_duration`. This is usefull when the remaining duration is unlinked from the original duration in the project settings - in these cases, the remaining duration can be different to the original duration in tasks that have not started.

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Fixed bug where the `start` property of the `TASK` class will return the early finish date rather than early start date if task is not started. [Issue 1](https://github.com/jjCode01/xerparser/issues/1)

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General Notes

* Added docstrings to more classes.
* Improved type validation.

Added

* Added `full_code` property to `ACCOUNT` class. This property returns the full path to the cost code including any parent codes. This property is now the basis for comparing `ACCOUNT` objects.

General Notes

* Small amount of code cleanup and refactoring.

Added

* Added `parent_acct_id` and `seq_num` attributes to `ACCOUNT` class.
* Added `parent` property to `ACCOUNT` class.

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