glib: Add missing (nullable) and (optional) annotations

Add various (nullable) and (optional) annotations which were missing
from a variety of functions. Also port a couple of existing (allow-none)
annotations in the same files to use (nullable) and (optional) as
appropriate instead.

Secondly, add various (not nullable) annotations as needed by the new
default in gobject-introspection of marking gpointers as (nullable). See
https://bugzilla.gnome.org/show_bug.cgi?id=729660.

This includes adding some stub documentation comments for the
assertion macro error functions, which weren’t previously documented.
The new comments are purely to allow for annotations, and hence are
marked as (skip) to prevent the symbols appearing in the GIR file.

https://bugzilla.gnome.org/show_bug.cgi?id=719966

gobject/gtype.h

@@ -629,7 +629,7 @@ struct _GTypeQuery
  * This macro should only be used in type implementations.
  * 
  * Since: 2.4
- * Returns: a pointer to the private data structure
+ * Returns: (not nullable): a pointer to the private data structure
  */
 #define G_TYPE_INSTANCE_GET_PRIVATE(instance, g_type, c_type)   ((c_type*) g_type_instance_get_private ((GTypeInstance*) (instance), (g_type)))
 
@@ -646,7 +646,7 @@ struct _GTypeQuery
  * This macro should only be used in type implementations.
  * 
  * Since: 2.24
- * Returns: a pointer to the private data structure
+ * Returns: (not nullable): a pointer to the private data structure
  */
 #define G_TYPE_CLASS_GET_PRIVATE(klass, g_type, c_type)   ((c_type*) g_type_class_get_private ((GTypeClass*) (klass), (g_type)))
 
@@ -746,7 +746,7 @@ int                   g_type_get_instance_count      (GType            type);
 /* --- type registration --- */
 /**
  * GBaseInitFunc:
- * @g_class: The #GTypeClass structure to initialize
+ * @g_class: (type GObject.TypeClass): The #GTypeClass structure to initialize
  * 
  * A callback function used by the type system to do base initialization
  * of the class structures of derived types. It is called as part of the
@@ -755,23 +755,23 @@ int                   g_type_get_instance_count      (GType            type);
  * For example, class members (such as strings) that are not sufficiently
  * handled by a plain memory copy of the parent class into the derived class
  * have to be altered. See GClassInitFunc() for a discussion of the class
- * intialization process.
+ * initialization process.
  */
 typedef void   (*GBaseInitFunc)              (gpointer         g_class);
 /**
  * GBaseFinalizeFunc:
- * @g_class: The #GTypeClass structure to finalize
+ * @g_class: (type GObject.TypeClass): The #GTypeClass structure to finalize
  * 
  * A callback function used by the type system to finalize those portions
  * of a derived types class structure that were setup from the corresponding
  * GBaseInitFunc() function. Class finalization basically works the inverse
- * way in which class intialization is performed.
- * See GClassInitFunc() for a discussion of the class intialization process.
+ * way in which class initialization is performed.
+ * See GClassInitFunc() for a discussion of the class initialization process.
  */
 typedef void   (*GBaseFinalizeFunc)          (gpointer         g_class);
 /**
  * GClassInitFunc:
- * @g_class: The #GTypeClass structure to initialize.
+ * @g_class: (type GObject.TypeClass): The #GTypeClass structure to initialize.
  * @class_data: The @class_data member supplied via the #GTypeInfo structure.
  * 
  * A callback function used by the type system to initialize the class
@@ -874,7 +874,7 @@ typedef void   (*GClassInitFunc)             (gpointer         g_class,
 					      gpointer         class_data);
 /**
  * GClassFinalizeFunc:
- * @g_class: The #GTypeClass structure to finalize
+ * @g_class: (type GObject.TypeClass): The #GTypeClass structure to finalize
  * @class_data: The @class_data member supplied via the #GTypeInfo structure
  * 
  * A callback function used by the type system to finalize a class.
@@ -890,7 +890,8 @@ typedef void   (*GClassFinalizeFunc)         (gpointer         g_class,
 /**
  * GInstanceInitFunc:
  * @instance: The instance to initialize
- * @g_class: The class of the type the instance is created for
+ * @g_class: (type GObject.TypeClass): The class of the type the instance is
+ *    created for
  * 
  * A callback function used by the type system to initialize a new
  * instance of a type. This function initializes all instance members and
@@ -908,7 +909,7 @@ typedef void   (*GInstanceInitFunc)          (GTypeInstance   *instance,
 					      gpointer         g_class);
 /**
  * GInterfaceInitFunc:
- * @g_iface: The interface structure to initialize
+ * @g_iface: (type GObject.TypeInterface): The interface structure to initialize
  * @iface_data: The @interface_data supplied via the #GInterfaceInfo structure
  * 
  * A callback function used by the type system to initialize a new
@@ -922,7 +923,7 @@ typedef void   (*GInterfaceInitFunc)         (gpointer         g_iface,
 					      gpointer         iface_data);
 /**
  * GInterfaceFinalizeFunc:
- * @g_iface: The interface structure to finalize
+ * @g_iface: (type GObject.TypeInterface): The interface structure to finalize
  * @iface_data: The @interface_data supplied via the #GInterfaceInfo structure
  * 
  * A callback function used by the type system to finalize an interface.
@@ -934,7 +935,8 @@ typedef void   (*GInterfaceFinalizeFunc)     (gpointer         g_iface,
 /**
  * GTypeClassCacheFunc:
  * @cache_data: data that was given to the g_type_add_class_cache_func() call
- * @g_class: The #GTypeClass structure which is unreferenced
+ * @g_class: (type GObject.TypeClass): The #GTypeClass structure which is
+ *    unreferenced
  * 
  * A callback function which is called when the reference count of a class 
  * drops to zero. It may use g_type_class_ref() to prevent the class from
@@ -954,7 +956,8 @@ typedef gboolean (*GTypeClassCacheFunc)	     (gpointer	       cache_data,
 /**
  * GTypeInterfaceCheckFunc:
  * @check_data: data passed to g_type_add_interface_check()
- * @g_iface: the interface that has been initialized
+ * @g_iface: (type GObject.TypeInterface): the interface that has been
+ *    initialized
  * 
  * A callback called after an interface vtable is initialized.
  * See g_type_add_interface_check().