Added MIDI pattern (#5)

patterns/midi.hexpat

@@ -0,0 +1,95 @@
+#pragma MIME audio/midi
+
+using Delta = u8;
+using NoteValue = u8;
+using Velocity = u8;
+using EOF = u8;
+
+// this is just for debugging midi file generation
+// I'm testing a known good file against a bad one
+// the file is hard coded in file format 0, and if
+// you're expecting meta events anywhere add a specific
+// call for those
+// https://www.music.mcgill.ca/~ich/classes/mumt306/StandardMIDIfileformat.html
+
+enum NoteEvent : u8 {
+    NoteOn = 0x90,
+    NoteOff = 0x80
+};
+
+enum MetaFlag : u16 {
+    Footer = 0xFF2F,
+    KeySigEvent = 0xFF59,
+    TimeSigEvent = 0xFF58,
+    TempoEvent = 0xFF51,
+    TrackNameEvent = 0xFF03
+};
+
+enum HeaderFlag : u32 {
+    MThd = 0x4D546864
+};
+
+enum TrackChunk : u32 {
+    MTrk = 0x4D54726B
+};
+
+struct TimeSigEvent {
+    Delta delta;
+    MetaFlag flag;
+    u16 numerator;
+    u8 denominator;
+    u8 ticks_per_click; // not used
+    u8 thirty_second_notes_per_crotchet;
+};
+
+struct KeySigEvent {
+    Delta delta;
+    MetaFlag flag;
+    u16 key;
+    u8 mode;
+};
+
+struct TempoEvent {
+    Delta delta;
+    MetaFlag flag;
+    u32 micro_seconds_per_click; // default 1 million
+};
+
+struct TrackNameEvent {
+    Delta delta;
+    MetaFlag flag;
+    u8 length;
+    u8 text;
+};
+
+struct Note {
+    Delta delta;
+    NoteEvent ne;
+    NoteValue note;
+    Velocity vel;
+};
+
+struct HeaderChunk {
+    HeaderFlag flag;
+    u32 length;
+    u16 mode;
+    u16 num_tracks;
+    u16 ticks_per_quarter;
+    TrackChunk chunk;
+    u32 track_length;
+};
+
+struct Footer {
+	Delta d;
+	MetaFlag m;
+	EOF eof;
+};
+
+struct MidiFile {
+    HeaderChunk header;
+    // whatever meta flags can be in here
+    Note notes[12]; //however many notes you're looking at
+    Footer f;
+};
+
+MidiFile midi_file @ 0x00;