Add --image-scale option for setting the scale factor of rendered image(s)

[yhatt]

Added --image-scale option to set the scale factor of rendered image (up to x10).

marp markdown.md --image png --image-scale 2

Marp Core has built-in themes were sized by 1280x720. If specified --image(s) png --image-scale 2, Marp CLI will render the image that has sized 2560x1440.

It is also available for PPTX conversion. By default, Marp CLI with --pptx option will prerender images by the scale factor x2.5. This change may increase the output size of PPTX but will improve shaggy of rendered images on presenting in full-screen.

If you want the previous rendering, you can set --image-scale 1 together with --pptx option.

marp markdown.md --pptx --image-scale 1

ToDo

• Update documentation