Update .gitignore

Adding .pdfs
Updated the VO hierarchy, added individuals to SerializationFormat and added individuals to MaturityLevel to get at a basic definition
Merge branch 'master' of https://github.com/AndreaWesterinen/vocref-1
Fixing
Merge pull request #13 from AndreaWesterinen/master

Fixing up the VO hierarchy and adding a few individuals; Also cleaned up the editorialNote annotation property