Add a a test for max size XLSX files
Fix file path
Switch to iterators for openpyxl

http://stackoverflow.com/questions/21875249/memory-error-using-openpyxl-
and-large-data-excels
Switch to Workbook.iter_rows() and add warning
Extend the build timeout
Merge pull request #171 from jacebrowning/feature/handle-large-xlsx

Handle large XLSX files