broke up some long docstrings
improved NCElement, added tests, travis
update .travis.yml
Update .travis.yml

changed cover-package
requirements.txt: fixed typo
ncclient/manager.py fixed more docstrings
Merge branch 'NCElement_xml_usability' of https://github.com/francisluong/ncclient into francisluong-NCElement_xml_usability
Merge branch 'francisluong-NCElement_xml_usability'