add vamp-plugin example lua script

scripts/_vamp_example.lua

@@ -0,0 +1,49 @@
+ardour { ["type"] = "Snippet", name = "Vamp Plugin Example" }
+
+function factory () return function ()
+	local sel = Editor:get_selection ()
+
+	local vamp = ARDOUR.LuaAPI.Vamp("libardourvampplugins:dBTP", Session:nominal_frame_rate())
+	print (vamp:plugin():getName())
+
+	-- for each selected region
+	for r in sel.regions:regionlist ():iter () do
+		print ("Region:", r:name ())
+
+		-- run the plugin, analyze the first channel of the audio-region
+		vamp:analyze (r:to_readable (), 0, nil)
+
+		-- get analysis results
+		local f = vamp:plugin ():getRemainingFeatures ()
+
+		-- f is-a Vamp::Plugin::FeatureSet  aka  std::map<int, Vamp::Plugin::FeatureList>
+		for id, featlist in f:iter () do
+			print (id, featlist)
+		end
+
+		-- get the first FeatureList
+		local featurelist = f:table()[0]
+		-- Vamp::Plugin::FeatureList is a typedef for std::vector<Feature>
+		for feat in featurelist:iter () do
+			print ("-", feat.label)
+		end
+
+		-- get the first feature..
+		local feature = featurelist:at(0)
+		-- ..and the values of the feature, which is-a std::vector<float>
+		local values = feature.values
+		-- iterate over the std::vector<float>
+		for val in values:iter () do
+			print ("*", val)
+		end
+
+		-- access the first element of Vamp::Plugin::Feature's "values" vector
+		local value = values:at(0)
+		-- in case of libardourvampplugins:dBTP that's the true-peak
+		local dbtp = 20 * math.log (value) / math.log(10)
+		print (string.format ("Region '%s': %.2f dBTP", r:name (), dbtp))
+
+		-- reset the plugin
+		vamp:reset ()
+	end
+end end