MO3 now with MPTM support

[Saga Musix]

The MO3 encoder has been updated for the first time in a long time, and Ian and me sat down to extend the format to allow all OpenMPT extensions to be stored in it. This also includes practically all MPTM extensions. MO3 2.4.1 has now been released and contains all those changes. The current stable OpenMPT version does of course not read them yet, but you can replace the existing unmo3.dll with the one from the "UNMO3 Library" download on that page to take advantage of the new features before the next OpenMPT release.