Add 2 modules

[juancarlospaco]

• Add 2 new modules, xpm.nim and netpbm.nim.
• Half the code is Tests approx, all functions are asserted.
• Only uses system.nim, no imports, does not use std lib, easy to maintain.
• runnableExamples with static: and doAssert.
• Documentation with Examples and Links. changelog.md entry.
• Works at compile-time and JavaScript.
• All functions are func, except 1 that does the I/O.
• Tiny func of 3 ~ 5 lines, simple code, simple API.
• Functionality can be extended with sequtils by the user.
• Examples render 6 small fractals at compile-time to mimic a real-world like usage.
• Only adds ~300 lines where half are test, adding 5 image formats, so I think it worth it.

Random example use cases

• Generate Icons of arbitrary sizes instead of bundling them in binaries and installers.
• Generate patterns on client-side browser instead of transferring them over internet.
• Render QR codes, Bar codes, Icons, visual reports, simple diagrams for documentation, etc.
• Plot charts with data of any kind on any target.
• Anything image related, good addition to SVG and HTML that std lib already can do.

Format

Image format is loss-less and human-readable, UTF-8 but fits ASCII,
is also valid C source code, can be embedded in C, supports millions of colors and transparency.

Links

• Rust lang one https://docs.rs/image/latest/image/pnm/struct.PNMEncoder.html
• Python also has a module to draw images on std lib.
• Spec https://en.wikipedia.org/wiki/X_PixMap
• Spec https://en.wikipedia.org/wiki/Netpbm_format

Examples with Std Lib only

[krux02]

• You don't need var for ref types (unless you want to set the pointer itself). Also the var prefix binds stronger than |, so the ast for your arguments looks like this: (Infix (Infix (Ident "|") (VarTy (Ident "PBM")) (Ident "PGM"))), not as you might think(VarTy (Infix (Ident "|") (Ident "PBM") (Ident "PGM"))).
• Using types composed with | makes the proc implicitly generic with code instantiation per type, even though the implementation is completely identical, no generic code instantiation needed, except for the $ and the writeFile proc. Please don't use generics for this module.
• Please don't use ref types if you don't need to, and I don't see the need for ref types here.
• Please don't use seq[seq[byte]] for image data. This has too much allocation overhead. Use one flat seq[byte] and compute the indices. This is also the format that for example OpenGL needs when you pass image data to it.

I Didn't even start yet to look into the procedures and question if they are worth to be added to the standard library. Why don't you make this just a nimble package?

[dom96]

I don't think this belongs to the stdlib.