validating the enml using the dtd

[Jaymon]

• http://code.activestate.com/recipes/220472-validating-xml-with-external-dtds-using-xmlproc/
• https://stackoverflow.com/questions/31769514/how-do-i-validate-xml-against-dtd-using-python

This hasn't seemed to be a problem so far but Evernote's docs recommend validating the .content against the DTD locally, so I could do that in the future, I punted on it because I didn't want to install a whole bunch more dependencies

see also:

• https://docs.python.org/2.7/library/xml.html