Add m3u support

[retropieuser]

have added in a check if the Command line file if it's an M3U file then take the first two files and use them as disk 1 & 2

[retropieuser]

Apologies for the slightly untidy multi commits, am a bit new to the best way to add changes on GitHub

[bubio]

Thanks for adding this😊. I hadn’t considered M3U support for XM8 before, but it makes sense for frontends and multi-disk titles.

I’d like to keep the macOS deployment target at 10.13. std::filesystem requires a newer macOS deployment target with Apple’s libc++, but this feature only needs simple path joining for M3U entries.

Could you avoid std::filesystem and keep the deployment target at 10.13? Something like this should be enough here:

std::string ParentDirectory(const std::string& path)
{
    const std::string::size_type slash = path.find_last_of("/\\");
    if (slash == std::string::npos) {
        return "";
    }
    return path.substr(0, slash + 1);
}

std::string ResolveM3UEntry(const std::string& baseDir, const std::string& entry)
{
    if (entry.empty()) {
        return entry;
    }
    if (entry[0] == '/' || entry[0] == '\\') {
        return entry;
    }
    if (entry.size() >= 2 && std::isalpha(static_cast<unsigned char>(entry[0])) && entry[1] == ':') {
        return entry;
    }
    return baseDir + entry;
}

Then LoadM3U() can use ParentDirectory(path) once and append relative entries without requiring .

[retropieuser]

no problem, have added in your changes and functionality is still the same, although I am on a later OSX build so I can't test 10.13 fully