[Feature request] Add ability to set card size

[IgorGakhov]

Good day! It seems like it would be a great and much needed addition.

Example: card_width - Set the card's width manually (number)

- If the feature request is approved, would you be willing to submit a PR? - No :pensive:

[simbafs]

The output cards is svg, you can rescale them as you need.

[cottinisimone]

And adding card_height might be a good idea too.

@simbafs you are right but add those two args might be extremely useful when embedding svgs in markdown files