Build 3.5.0.73 of xlsgen makes a number of improvements in speed for working with XLSX files.

Included is :
- Faster reading of depending parts when there are many depending parts (for instance many external references in spreadsheets).
- Faster opening in Excel of files created/updated by xlsgen by writing additional metadata in the file such as spreadsheet dimensions and row spans.
- Automatic removal of useless cells, whose number may be arbitrary (and a consequence of Excel creating orphans) which lowers the file size as well as the reopening speed in Excel
- Removal of rows referencing useless cells. Again the amount being removed is arbitrary and can mount to millions.
- Better handling of out of memory scenarios (2GB is the maximum working set per process on WIN32 systems)