Syncing with the new MMIF spec

[keighrim]

fixes #320

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.71%. Comparing base (711bc35) to head (c9b2a31).
Report is 71 commits behind head on develop.

Files with missing lines	Patch %	Lines
mmif/serialize/view.py	90.00%	1 Missing ⚠️
mmif/utils/text_document_helper.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #321      +/-   ##
===========================================
- Coverage    87.74%   87.71%   -0.03%     
===========================================
  Files           13       13              
  Lines         1648     1661      +13     
===========================================
+ Hits          1446     1457      +11     
- Misses         202      204       +2     

Flag	Coverage Δ
unittests	87.71% <88.88%> (-0.03%)	⬇️

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