Enable shared libs

Author: jschueller

appveyor.yml

@@ -20,8 +20,8 @@ before_build:
     - cd c:\projects\jsoncpp
     - cmake --version
     - set PATH=C:\Program Files (x86)\MSBuild\14.0\Bin;%PATH%
-    - if %PLATFORM% == Win32 cmake .
-    - if %PLATFORM% == x64 cmake -G "Visual Studio 12 2013 Win64" .
+    - if %PLATFORM% == Win32 cmake -DBUILD_SHARED_LIBS=ON .
+    - if %PLATFORM% == x64 cmake -G "Visual Studio 12 2013 Win64" -DBUILD_SHARED_LIBS=ON .
 
 build:
     project: jsoncpp.sln        # path to Visual Studio solution or project