Implementation Level Parsing Fixes

There were problems when interpreting the transaction sets at the implementation guide level. This release should fix these issues.

There were additional tests added to try and capture any parsing errors.

A known limitation right now is that the functional group creation time is set to always generate 4 digits of precision (hour and minute) when writing, regardless of the actual precision used when reading. All sample files have had their GS05 element set to this level of precision.