Function find_file

pub fn find_file(
    file: &str,
    subdir: Option<&str>,
    extension: Option<&str>,
) -> Option<PathBuf>

Tries to find a file in standard locations:

• Fist try to find a file by full path (only if path is absolute)
• Then try XDG_CONFIG_HOME (e.g. ~/.config)
• Then try XDG_DATA_HOME (e.g. ~/.local/share/)
• Then try /usr/share/

Automatically append an extension if not presented.