Update stb_image and Image documentation

[kimci86]

Description

Updates stb_image.h and stb_image_write.h with latest version from stb.
The diffs seems to show that every line changed but that is because we used CRLF line endings instead of LF (probably by mistake).

Also updates Image::loadFromX methods documentation to mention every supported format.

This PR is related to this project card: https://github.com/SFML/SFML/projects/4#card-14010188

Tasks

• Tested on Linux
• Tested on Windows
• Tested on macOS
• Tested on iOS
• Tested on Android

How to test this PR?

There is not much to test besides compilation.
Anyways I made this example program to check that loading PNM images succeeds for supported format variants.

#include <SFML/Graphics.hpp>
#include <cassert>

int main()
{
    auto image = sf::Image{};
    assert(image.loadFromFile("logo.pnm"));
    assert(image.loadFromFile("logo.pgm"));
    assert(!image.loadFromFile("logo.pbm"));
    assert(!image.loadFromFile("logo_ascii.pnm"));
    assert(!image.loadFromFile("logo_ascii.pgm"));
}

Image files: logo.zip

[eXpl0it3r]

Thanks for doing this update! 🥳