If <dimension> not present, iterate over all rows and cols.
If <dimension> not present, iterate over all rows and cols.

Closes #26

warnes/readxl,NikhilMIT2013/readxl,nvoron23/readxl,NikhilMIT2013/readxl,rdoering/readxl,rdoering/readxl,nvoron23/readxl,warnes/readxl,pozypakya/readxl,pozypakya/readxl,NikhilMIT2013/readxl,warnes/readxl,rdoering/readxl,nvoron23/readxl,pozypakya/readxl