added VGM playback

doc/api.md

@@ -10,6 +10,7 @@
 * [love.filesystem](#lovefilesystem)
 * [love.audio](#loveaudio)
 * [love.event](#loveevent)
+* [love.vgm](#lovevgm)
 
 ##### [Objects](#objects-1)
 * [Image](#image)
@@ -38,6 +39,18 @@ Returns the amount of memory in kilobytes which is being used by LoveDOS. This
 includes the memory used by both the loaded assets and lua.
 
 
+### love.vgm
+VGM OPL2 playback
+
+##### love.vgm.VgmLoad(filename)
+Load (or replace) a VGM.
+
+##### love.vgm.VgmPlay()
+Start VGM playback.
+
+##### love.vgm.VgmStop()
+Stop VGM playback.
+
 ### love.graphics
 Provides functions for drawing lines, shapes, text and images.