Mpxj

* Added support for reading recurring exceptions from MPP and MSPDI files.
* Updated RecurringTask class interface (Note: this is a breaking API change)
* MSPDI writer now uses save version 14 by default (Note: this may affect applications which consume MSPDI files you generate)
* Correctly handle MSPDI files with Byte Order Marks.
* Handle MSPDI files with varying namespaces.
* Improve robustness Merlin file reader.
* Improve extraction of task start and finish dates from PMXML files only containing partial data.
* Prevent POI from closing the input stream when using UniversalProjectReader
* Fixed [Issue 321](https://sourceforge.net/p/mpxj/bugs/321): Cannot read mpp file using getProjectReader.

* Gracefully handle corrupt MPP files.
* Improve reading and writing slack values for MSPDI files.
* Improve activity hierarchy extraction from Phoenix files.
* Fixed [Issue 243](https://sourceforge.net/p/mpxj/bugs/243): MSPDI Slack values not correctly set while loading.

* Added support for reading Work Weeks from MPP files.
* Add support for calendar exception names for MPP and MSPDI files.
* Updated to use POI 3.17.
* Improve accuracy of calendar exception dates read from XER files and P6 database.
* Only write non-default user-defined field values to a PMXML file.
* Use Primavera P6 17.7 XML schema.
* Gracefully handle corrupt document summary information in MPP files.
* Don't duplicate exceptions when reading from an MSPDI file.
* Fixed [Issue 231](https://sourceforge.net/p/mpxj/bugs/231): MPP DataType: Non-unique enumeration value.
* Fixed [Issue 258](https://sourceforge.net/p/mpxj/bugs/258): Calendar Work Week missing from MPP data extraction.
* Fixed [Issue 318](https://sourceforge.net/p/mpxj/bugs/318): TimephasedWork Negative TotalAmount.
* Fixed [Issue 320](https://sourceforge.net/p/mpxj/bugs/320): Date conversion fails in PrimaveraReader.

* Gracefully handle incomplete records in XER files.

* Ensure all classes in the gem are required

* Provide Task.getEffectiveCalendar() method
* Populate missing finish dates in MSPDI files