Renamed config.h -> jansson_private_config.h

This is because it's really easy to get a name collission if compiling
Jansson as a subproject in a larger CMake project. If one project includes
several subprojects each having their own config.h, this will cause the
wrong file to be loaded.

src/strconv.c

@@ -5,9 +5,9 @@
 #include "jansson_private.h"
 #include "strbuffer.h"
 
-/* need config.h to get the correct snprintf */
+/* need jansson_private_config.h to get the correct snprintf */
 #ifdef HAVE_CONFIG_H
-#include <config.h>
+#include <jansson_private_config.h>
 #endif
 
 #if JSON_HAVE_LOCALECONV

src/utf.h

@@ -9,7 +9,8 @@
 #define UTF_H
 
 #ifdef HAVE_CONFIG_H
-#include <config.h>
+
+#include <jansson_private_config.h>
 
 #ifdef HAVE_INTTYPES_H
 /* inttypes.h includes stdint.h in a standard environment, so there's