add extension_list example (#281)

- Created an example of extension policy
- Added C# binding support of .NET framework 4.0 and created a Nuget
  spec for it.
- Added a pytest in python bindings to test the extension policy and the
  python binding
- Restructured the example and Csharp binding directories due to above
  changes.
- Added copyrights.
- Added a Windows workflow for .NET 4.0 build and test.

examples/server/input.json

@@ -0,0 +1,20 @@
+{
+    "servers": [
+        {"id": "app", "protocols": ["https", "ssh"], "ports": ["p1", "p2", "p3"]},
+        {"id": "db", "protocols": ["mysql"], "ports": ["p3"]},
+        {"id": "cache", "protocols": ["memcache"], "ports": ["p3"]},
+        {"id": "ci", "protocols": ["http"], "ports": ["p1", "p2"]},
+        {"id": "busybox", "protocols": ["telnet"], "ports": ["p1"]}
+    ],
+    "networks": [
+        {"id": "net1", "public": false},
+        {"id": "net2", "public": false},
+        {"id": "net3", "public": true},
+        {"id": "net4", "public": true}
+    ],
+    "ports": [
+        {"id": "p1", "network": "net1"},
+        {"id": "p2", "network": "net3"},
+        {"id": "p3", "network": "net2"}
+    ]
+}