add a new .sln file for Visual Studio 2015, since we are already using C# 6 features.

you don't think people will use Roslyn with Visual Studio 2012, do you?

shadowsocks-windows.sln

@@ -0,0 +1,32 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 14
+VisualStudioVersion = 14.0.24720.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "shadowsocks-csharp", "shadowsocks-csharp\shadowsocks-csharp.csproj", "{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "test", "test\test.csproj", "{45913187-0685-4903-B250-DCEF0479CD86}"
+	ProjectSection(ProjectDependencies) = postProject
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062} = {8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}
+	EndProjectSection
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|x86 = Debug|x86
+		Release|x86 = Release|x86
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}.Debug|x86.ActiveCfg = Debug|x86
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}.Debug|x86.Build.0 = Debug|x86
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}.Debug|x86.Deploy.0 = Debug|x86
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}.Release|x86.ActiveCfg = Release|x86
+		{8C02D2F7-7CDB-4D55-9F25-CD03EF4AA062}.Release|x86.Build.0 = Release|x86
+		{45913187-0685-4903-B250-DCEF0479CD86}.Debug|x86.ActiveCfg = Debug|x86
+		{45913187-0685-4903-B250-DCEF0479CD86}.Debug|x86.Build.0 = Debug|x86
+		{45913187-0685-4903-B250-DCEF0479CD86}.Release|x86.ActiveCfg = Release|x86
+		{45913187-0685-4903-B250-DCEF0479CD86}.Release|x86.Build.0 = Release|x86
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal