Put back Windows shared lib building

Author: CJCombrink

appveyor.yml

@@ -40,7 +40,7 @@ environment:
      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
      PLATFORM: x64
      CONFIGURATION: Release
-     BUILD_SHARED_LIBS: OFF
+     BUILD_SHARED_LIBS: ON
      BOOST_VERSION: 1.67.0
      LIBEVENT_VERSION: 2.1.8
      PYTHON_VERSION: 3.6