create branch 0.1.5
modify SpreadsheetFactory
modify test_spreadsheet_factory.py (skipped column)
update cell (test skip)
update_cell() is implemented after gdata-2.0.18
add updateCell to SpreadsheetFactory
release 0.1.5
Merge pull request #21 from HatsuneMiku/0.1.5

merge branch 0.1.5