add openpyxl to setup.py's install_requires
import global instead of packaged openpyxl
use new openpyxl Styles (see: groups.google.com/forum/#!topic/openpyxl-users/hdTAidKQVpE)
fix styling
consistent formatting
avoid "None" strings. @iurisilvio , is this the correct approach? Not sure if this is the correct place for such things...
reorder formats to put xlxx in front of dbf (dbf errored when trying to read xlsx files)
fall back to BytesIO to be consistent with tablib API