Use PEP8 style of asserts from nose.tools
Added tests for stoplist functions
PEP8: removed extra lines between methods
Use context manager for ignored exceptions
100% test coverage of function 'decode_html'
Removed unused function 'decode_entities_pp'
100% test coverage of function 'preprocess'
PEP8: added extra lines between functions
Removed unused import
Added utils package for utility functions
Don't import justext in setup.py file

Script ends with error if lxml is not already
installed.
More info at http://stackoverflow.com/a/2073599.
DOC: added info about PIP & updated installation