add Name field for Sheet
Merge pull request #29 from lunny/master

add Name field for Sheet
add test for google docs excel
Allow for manual calculation of the dimensions of a sheet if no DimensionRef is
provided in the worksheet.  Issue 30 occurs because this element is missing
from Google Docs XLSX output.
Typo fix
Merge pull request #31 from chrisglass/patch-1

Typo fix - cheers Chris Glass.