Use declare namespace syntax when possible

T4TS.Tests/Output/ModuleOutputAppenderTests.cs

@@ -45,6 +45,24 @@ public void TypescriptVersion090YieldsDeclareModule()
             appender.AppendOutput(module);
             Assert.IsTrue(sb.ToString().StartsWith("declare module "));
         }
+
+        [TestMethod]
+        public void TypescriptVersion150YieldsDeclareNamespace()
+        {
+            var sb = new StringBuilder();
+            var module = new TypeScriptModule
+            {
+                QualifiedName = "Foo"
+            };
+
+            var appender = new ModuleOutputAppender(sb, 0, new Settings
+            {
+                CompatibilityVersion = new Version(1, 5, 0)
+            });
+
+            appender.AppendOutput(module);
+            Assert.IsTrue(sb.ToString().StartsWith("declare namespace "));
+        }
 
         [TestMethod]
         public void DefaultTypescriptVersionYieldsDeclareModule()

T4TS/Outputs/ModuleOutputAppender.cs

@@ -34,8 +34,10 @@ private void BeginModule(TypeScriptModule module)
             {
                 if (Settings.CompatibilityVersion != null && Settings.CompatibilityVersion < new Version(0, 9, 0))
                     Output.Append("module ");
-                else
+                else if (Settings.CompatibilityVersion == null || Settings.CompatibilityVersion < new Version(1, 5, 0))
                     Output.Append("declare module ");
+                else
+                    Output.Append("declare namespace ");
 
                 Output.Append(module.QualifiedName);
                 Output.AppendLine(" {");