docs: Move the GIOError SECTION

Move it to a separate page as there’s no struct documentation to hang it
off.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3037

docs/reference/gio/error.md

@@ -0,0 +1,12 @@
+Title: GIOError
+SPDX-License-Identifier: LGPL-2.1-or-later
+SPDX-FileCopyrightText: 2007 A. Walton
+
+# GIOError
+
+Contains helper functions for reporting errors to the user.
+
+Functions for converting between different error reporting mechanisms:
+ * [func@Gio.io_error_from_errno]
+ * [func@Gio.io_error_from_file_error]
+

docs/reference/gio/gio.toml.in

@@ -43,6 +43,9 @@ content_files = [
   "overview.md",
   "file-attributes.md",
   "tls-overview.md",
+
+  "error.md",
+
   "dbus-error.md",
   "dbus-introspection.md",
   "dbus-name-owning.md",

docs/reference/gio/meson.build

@@ -230,6 +230,7 @@ expand_content_files = [
   'dbus-name-owning.md',
   'dbus-name-watching.md',
   'dbus-utils.md',
+  'error.md',
   'file-attributes.md',
   'migrating-gconf.md',
   'migrating-gdbus.md',

gio/gioerror.c

@@ -30,14 +30,6 @@
 #include <winsock2.h>
 #endif
 
-/**
- * SECTION:gioerror
- * @short_description: Error helper functions
- * @include: gio/gio.h
- *
- * Contains helper functions for reporting errors to the user.
- **/
-
 /**
  * g_io_error_quark:
  *