add a script to exercise varispeed playback

scripts/varispeed_callback.lua

@@ -0,0 +1,32 @@
+ardour {
+	["type"]    = "EditorHook",
+	name        = "Varispeed Test - 100ms Callback",
+	author      = "Ardour Lua Task Force",
+	description = "An example script that invokes a callback a every 0.1sec and modifies the transport speed",
+}
+
+function signals ()
+	s = LuaSignal.Set()
+	s:add (
+		{
+			[LuaSignal.LuaTimerDS] = true,
+		}
+	)
+	return s
+end
+
+function factory (params)
+	-- upindex variables
+	local cnt = 0
+	local speed = 0
+	local delta = 0.01
+	return function (signal, ref, ...)
+		cnt = (cnt + 1) % 5 -- divide clock: every half a second
+		if cnt == 0 then
+			if speed < -0.25 then delta = delta * -1 end
+			if speed >  0.25 then delta = delta * -1 end
+			speed = speed + delta
+			Session:request_transport_speed (speed)
+		end
+	end
+end