SVG support

Error loading presentation: 

could not load image 'logo.svg' at 13:1: image decoding: The image format could not be determined

I would have expected rastering of SVGs to PNGs to be handled internally by presentterm. This would be useful as I need to use the logo at different sizes on different slides.

Also, this would handle transparency better, as exporting to png from inkscape seems to do the wrong blending mode towards the terminal background colour (the image is getting a white fringe).

• presenterm 0.14.0
• Installed with cargo install
• Rust 1.87.0 (installed with rustup)
• Ubuntu 24.04 LTS