xml parsing of external files

[eshellman]

lxml is probably the thing to use here in place of the python default.

first install lxml.

then, instead of
from xml.etree import ElementTree
in external.py, use
from lxml.etree import ElementTree, XMLParser

parser = XMLParser(recover=True)
ElementTree.fromstring(opds.content, parser=parser)

[bdr99]

Sorry for the delay, I was away without internet access for a few days. I've created a PR #78 to use lxml with the recover=True parser option. Hopefully this will help in the future if Standard Ebooks has more xml syntax errors.