Add photo-to-line-art to Image Processing

[tim20010701]

Adds one entry to Image Processing.

• Package: photo-to-line-art — https://github.com/tim20010701/printable-coloring-page-toolkit
• Zero dependencies, plain ES module. Takes {data, width, height} pixel data and returns RGBA bytes; no canvas or DOM required, so it also runs in Node.
• Converts a photo into black-and-white line art via Sobel edge magnitude with adjustable detail, line thickness and inversion.
• Documented in the repo README, and tested: node --test runs 12 unit tests on synthetic pixel data (no browser or image files needed) — currently 12 passing, 0 failing.
• MIT licensed.

I have searched the list and photo-to-line-art is not already present.

Disclosure: I am the author of this package.

[gokaygurcan]