refs #27: added a test showing how an sdt tag should be handled.
refs #27: correctly handle sdt tags (including break separating)
Merge branch 'issue_25' into issue_27

Conflicts:
	pydocx/DocxParser.py
Merge branch 'master' into issue_27
Merge pull request #27 from OpenScienceFramework/issue_27

Documents with sdt tags break content ordering