Created a new solution for .NET Core.

runtime/CSharp/runtime/CSharp/Antlr4.DotNetCore.sln

@@ -0,0 +1,22 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 14
+VisualStudioVersion = 14.0.25420.1
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{8BB2217D-0F2D-49D1-97BC-3654ED321F3B}") = "Antlr4.Runtime.DotNetCore", "Antlr4.Runtime.DotNetCore.xproj", "{12962409-846E-4B80-933A-BC484D264132}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{12962409-846E-4B80-933A-BC484D264132}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{12962409-846E-4B80-933A-BC484D264132}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{12962409-846E-4B80-933A-BC484D264132}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{12962409-846E-4B80-933A-BC484D264132}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal

runtime/CSharp/runtime/CSharp/project.json

@@ -1,6 +1,8 @@
 {
   "buildOptions": {
-    "define": [ "DEBUG", "TRACE", "DOTNETCORE" ]
+    "define": [ "DEBUG", "TRACE", "DOTNETCORE" ],
+    "keyFile": "../Antlr4.snk",
+    "xmlDoc": true
   },
   "dependencies": {
     "NETStandard.Library": "1.6.0"