allow PDF export options

[ogura]

Fixed an error when calling the Libreconv.convert method with a pdf export option.

execute with pdf export option example:

Libreconv.convert(input_path, output_path, nil, 'pdf:calc_pdf_Export:{"SelectPdfVersion" {"type":"long","value":"15"}}')

The current version gives an error message:

Libreconv::ConversionFailedError (Conversion failed! Output: "convert /tmp/xxxx.xlsx -> /tmp/d20230530-1-a3mspb/xxxx.pdf using filter : calc_pdf_Export:{\"SelectPdfVersion\":{\"type\":\"long\",\"value\":\"1\"}}", Error: ""):

PDF export options is a feature added in the LibreOffice 7.4.
references:

• https://vmiklos.hu/blog/pdf-convert-to.html
• https://wiki.documentfoundation.org/ReleaseNotes/7.4

[ogura]

duplicate PR #35