start API cleanup by moving private headers and data structures into private/ include directory

libs/freetdm/src/hashtable.c

@@ -31,7 +31,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "freetdm.h"
+#include "private/ftdm_core.h"
 #include "hashtable.h"
 #include "hashtable_private.h"
 #include <stdlib.h>