Function run 

pub fn run(
    rules: &FontAtlas,
    command: &str,
    font_paths: &[PathBuf],
    wides: &[WideFont],
    out_dir: &Path,
    chars: &AtlasChars,
) -> Result<String, String>

Runs the command: reads the fonts at font_paths (the first is the font; the rest add glyphs to it) and the wide fonts wides, each its own set (one set once), and writes the glyphs chars wants to atlas.png, atlas.ron and atlas_1bit.bin in out_dir. Fails if the result lacks a glyph rules require; a character the text uses that the fonts lack is named in the summary, not a failure. command is what atlas.ron’s header calls the tool.