Fixes for .NET Core build

src/api/dotnet/Z3Exception.cs

@@ -21,11 +21,13 @@ using System;
 
 namespace Microsoft.Z3
 {
-  /// <summary>
-  /// The exception base class for error reporting from Z3
-  /// </summary>
+    /// <summary>
+    /// The exception base class for error reporting from Z3
+    /// </summary>
+#if !DOTNET_CORE
   [Serializable]
-  public class Z3Exception : Exception
+#endif
+    public class Z3Exception : Exception
   {
     /// <summary>
     /// Constructor.

src/api/dotnet/core/README.txt

@@ -0,0 +1,9 @@
+Z3 API for .NET Core
+
+Z3's .NET API uses Code Contracts, which are not included in .NET Core. The
+enclosed file called DummyContracts.cs provides stubs for the Code Contracts
+functions, so that the API will compile, but not perform any contract
+checking. To build this using .NET core, run (in this directory):
+
+dotnet restore
+dotnet build project.json

src/api/dotnet/core/project.json

@@ -4,7 +4,8 @@
         "debugType": "portable",
         "emitEntryPoint": false,
         "outputName": "Microsoft.Z3",
-        "compile": [ "../*.cs", "*.cs" ]
+        "compile": [ "../*.cs", "*.cs" ],
+        "define": ["DOTNET_CORE"]
     },
     "dependencies": { },
     "frameworks": {