refs #96: Added tests showing the problems with external images.
Merge branch 'master' into issue_96

Conflicts:
	pydocx/tests/test_docx.py
refs #96: Fixed the broken test with external images.
refs #96: Update note.
refs #96: Utility function added.
Merge pull request #96 from CenterForOpenScience/issue_96

Documents with external images are ignored