girepository: Add Header for Version Macros

This adds a header to the girepository library, which is then included
either directly or indirectly by the other headers so that all the public
symbols (and the 2 symbols in gitypelib-internal.h used by the tools) are
decorated by a macro, that can later be used to export the symbols and also
to be used to display compile-time warnings for usage of deprecated APIs,
which is like what is now being done in GLib (and GTK+, Clutter, and so
on).

This marks the first step that we begin to stop depending on the .symbols/
.def files to export the symbols.

https://bugzilla.gnome.org/show_bug.cgi?id=732669

gifunctioninfo.h

@@ -40,9 +40,17 @@ G_BEGIN_DECLS
 #define GI_IS_FUNCTION_INFO(info) \
     (g_base_info_get_type((GIBaseInfo*)info) ==  GI_INFO_TYPE_FUNCTION)
 
+
+GI_AVAILABLE_IN_ALL
 const gchar *           g_function_info_get_symbol     (GIFunctionInfo *info);
+
+GI_AVAILABLE_IN_ALL
 GIFunctionInfoFlags     g_function_info_get_flags      (GIFunctionInfo *info);
+
+GI_AVAILABLE_IN_ALL
 GIPropertyInfo *        g_function_info_get_property   (GIFunctionInfo *info);
+
+GI_AVAILABLE_IN_ALL
 GIVFuncInfo *           g_function_info_get_vfunc      (GIFunctionInfo *info);
 
 /**
@@ -51,6 +59,8 @@ GIVFuncInfo *           g_function_info_get_vfunc      (GIFunctionInfo *info);
  * TODO
  */
 #define G_INVOKE_ERROR (g_invoke_error_quark ())
+
+GI_AVAILABLE_IN_ALL
 GQuark g_invoke_error_quark (void);
 
 /**
@@ -72,6 +82,8 @@ typedef enum
   G_INVOKE_ERROR_ARGUMENT_MISMATCH
 } GInvokeError;
 
+
+GI_AVAILABLE_IN_ALL
 gboolean              g_function_info_invoke         (GIFunctionInfo *info,
 						      const GIArgument  *in_args,
 						      int               n_in_args,