Add generic event module with begin and end times.

Add module for converting events to schedule.

lib/midi_tools/event.ex

@@ -0,0 +1,27 @@
+defmodule MIDITools.Event do
+  defmodule Note do
+    defstruct channel: 0, tone: 0, start_time: 0, end_time: 0, velocity: 0
+
+    def new(channel, tone, start_time, end_time, velocity) do
+      %__MODULE__{
+        channel: channel,
+        tone: tone,
+        start_time: start_time,
+        end_time: end_time,
+        velocity: velocity
+      }
+    end
+  end
+
+  def convert(%Note{
+        channel: channel,
+        tone: tone,
+        start_time: start_time,
+        end_time: end_time,
+        velocity: velocity
+      }) do
+    note_on = MIDISynth.Command.note_on(channel, tone, velocity)
+    note_off = MIDISynth.Command.note_off(channel, tone)
+    [{start_time, note_on}, {end_time, note_off}]
+  end
+end

lib/midi_tools/schedule.ex

@@ -0,0 +1,10 @@
+defmodule MIDITools.Schedule do
+  def convert_events(events) do
+    events
+    |> Enum.flat_map(&MIDITools.Event.convert/1)
+    |> Enum.reduce(%{}, fn {time, midi}, acc ->
+      Map.update(acc, time, midi, &<<midi::binary, &1::binary>>)
+    end)
+    |> Enum.sort()
+  end
+end