Fixed some bugs that manifest with recent versions of midilib (MIDI::Array was being used inside MTK::MIDI module, so we either need to refer to standard Array as ::Array or use something more flexible like Enumerable). Appears to have been introduced with this change: https://github.com/jimm/midilib/commit/2274bb0d7fb2dd33a93f2403a7cbc4e2079589ee