Adding images directly from reference

[ft-lie]

When generating excel files with images that are already generated in the script, adding them to a temp file seems unnecessary.

I have added $file as an option to add the image directly . I'll send a Pull request shortly.

(Mainly my first pull request, so pls be gentle if I screwed it all up).

my $png = make_png(); #returning image, not filename
$worksheet1->insert_image( 'A1', \$png);

[jmcnamara]

Thanks I'll add support for images from a buffer at some point. The interface and behaviour will probably be like the Python version of Excel::Writer::XLSX:

worksheet.insert_image('B5', 'python.png', {'image_data': image_data})

See: https://xlsxwriter.readthedocs.io/worksheet.html#worksheet-insert-image.