Add support for static properties and methods (#28)

* x

* Add support for static properties and methods.

tests/ProxyInterfaceSourceGeneratorTests/Source/Human.cs

@@ -1,12 +1,7 @@
 namespace ProxyInterfaceSourceGeneratorTests.Source
 {
-    public class Human : Animal
+    public class Human
     {
         public bool IsAlive { get; set; }
     }
-
-    public class Animal
-    {
-        public bool X { get; set; }
-    }
 }