Fission dotnet 2.0 env (#337)

Adding a new dotnet environment, supporting dotnet core 2.0.

Project structure changed. Project.json was abandoned. Project.csproj is now used.

examples/dotnet20/requestbody.cs

@@ -0,0 +1,24 @@
+using System.IO;
+using System.Runtime.Serialization.Json;
+using Fission.DotNetCore.Api;
+
+public class FissionFunction
+{
+    public string Execute(FissionContext context)
+    {
+        var person = Person.Deserialize(context.Request.Body);
+        return $"Hello, my name is {person.Name} and I am {person.Age} years old.";
+    }
+}
+
+public class Person
+{
+    public string Name { get; set; }
+    public int Age { get; set; }
+
+    public static Person Deserialize(Stream json)
+    {
+        var serializer = new DataContractJsonSerializer(typeof(Person));
+        return (Person)serializer.ReadObject(json);
+    }
+}