add type page for 'playable'

docs/types/playable.md

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+# playable
+
+The **playable** data object provides a common format to play tones, melodies, and songs. Each of these music sources are created in different ways but are transformed into playable objects so that a single playback method is used to [play](/refernece/music/play) them.
+
+## Music sources for playable objects
+
+The blocks used to create playable music sources are the following:
+
+### Tone
+
+A tone is a musical note, or a sound frequency, and a duration. The duration is often set as the length of a `beat`.
+
+```block
+music.tonePlayable(262, music.beat(BeatFraction.Whole))
+```
+
+### Melody
+
+Melodies are a series of notes and a tempo to play them at.
+
+```block
+music.stringPlayable("D F E A E A C B ", 120)
+```
+
+## Play the music
+
+In your programs, you can simply use the ``||music:play||`` blocks for each playable object. Like this one for tone:
+
+```block
+music.play(music.tonePlayable(262, music.beat(BeatFraction.Whole)), music.PlaybackMode.UntilDone)
+```
+
+## Example
+
+Put 2 different playable music sources in an array. Play one after the other.
+
+```blocks
+let playables = [
+music.tonePlayable(262, music.beat(BeatFraction.Whole)),
+music.stringPlayable("D F E A E A C B ", 120)
+]
+for (let someMusic of playables) {
+    music.play(someMusic, music.PlaybackMode.UntilDone)
+    basic.pause(500)
+}
+```
+
+## See also
+
+[play](/reference/music/play), [tone playable](/reference/music/tone-playable),
+[string playable](/reference/music/string-playable)