cmake scripts enhancements
I'd like to propose two changes to cmake script, but before making PR I'd like to ask what you think about it.
FindFreetype.cmake - the version of this file distributed with cmake does more robust search for headers and library. It'd be easy to replace or remove this script from libgd unless there are some essential customizations. I think there are none, but I may be wrong.
more control what is built: options BUILD_SHARED_LIBRARY, BUILD_STATIC_LIBRARY, BUILD_PROGRAMS