* Fix failure when parsing xlsx with drawing having double (redefined) attributes
* Fix failure when parsing xlsx with drawing having double (redefined) attributes
* Fix#853 when loading and saving XLSX file with empty drawing cause corrupted output file. Store empty drawing as unparsed entity and save it as is when saving the file.
* Fix code style
When describing a cell, the cell reference (r="A1") is optional.
When not present, we should just increment the index of the last processed row.
Fixes#201Closes#225
