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

glib/ghash.c

@@ -767,8 +767,8 @@ g_hash_table_iter_init (GHashTableIter *iter,
 /**
  * g_hash_table_iter_next:
  * @iter: an initialized #GHashTableIter
- * @key: (allow-none): a location to store the key, or %NULL
- * @value: (allow-none): a location to store the value, or %NULL
+ * @key: (out) (optional): a location to store the key
+ * @value: (out) (nullable) (optional): a location to store the value
  *
  * Advances @iter and retrieves the key and/or value that are now
  * pointed to as a result of this advancement. If %FALSE is returned,
@@ -1155,8 +1155,9 @@ g_hash_table_lookup (GHashTable    *hash_table,
  * g_hash_table_lookup_extended:
  * @hash_table: a #GHashTable
  * @lookup_key: the key to look up
- * @orig_key: (allow-none): return location for the original key, or %NULL
- * @value: (allow-none): return location for the value associated with the key, or %NULL
+ * @orig_key: (allow-none): return location for the original key
+ * @value: (out) (optional) (nullable): return location for the value associated
+ * with the key
  *
  * Looks up a key in the #GHashTable, returning the original key and the
  * associated value and a #gboolean which is %TRUE if the key was found. This
@@ -1821,8 +1822,8 @@ g_hash_table_get_values (GHashTable *hash_table)
 
 /**
  * g_str_equal:
- * @v1: a key
- * @v2: a key to compare with @v1
+ * @v1: (not nullable): a key
+ * @v2: (not nullable): a key to compare with @v1
  *
  * Compares two strings for byte-by-byte equality and returns %TRUE
  * if they are equal. It can be passed to g_hash_table_new() as the
@@ -1847,7 +1848,7 @@ g_str_equal (gconstpointer v1,
 
 /**
  * g_str_hash:
- * @v: a string key
+ * @v: (not nullable): a string key
  *
  * Converts a string to a hash value.
  *
@@ -1922,8 +1923,8 @@ g_direct_equal (gconstpointer v1,
 
 /**
  * g_int_equal:
- * @v1: a pointer to a #gint key
- * @v2: a pointer to a #gint key to compare with @v1
+ * @v1: (not nullable): a pointer to a #gint key
+ * @v2: (not nullable): a pointer to a #gint key to compare with @v1
  *
  * Compares the two #gint values being pointed to and returns
  * %TRUE if they are equal.
@@ -1946,7 +1947,7 @@ g_int_equal (gconstpointer v1,
 
 /**
  * g_int_hash:
- * @v: a pointer to a #gint key
+ * @v: (not nullable): a pointer to a #gint key
  *
  * Converts a pointer to a #gint to a hash value.
  * It can be passed to g_hash_table_new() as the @hash_func parameter,
@@ -1966,8 +1967,8 @@ g_int_hash (gconstpointer v)
 
 /**
  * g_int64_equal:
- * @v1: a pointer to a #gint64 key
- * @v2: a pointer to a #gint64 key to compare with @v1
+ * @v1: (not nullable): a pointer to a #gint64 key
+ * @v2: (not nullable): a pointer to a #gint64 key to compare with @v1
  *
  * Compares the two #gint64 values being pointed to and returns
  * %TRUE if they are equal.
@@ -1988,7 +1989,7 @@ g_int64_equal (gconstpointer v1,
 
 /**
  * g_int64_hash:
- * @v: a pointer to a #gint64 key
+ * @v: (not nullable): a pointer to a #gint64 key
  *
  * Converts a pointer to a #gint64 to a hash value.
  *
@@ -2008,8 +2009,8 @@ g_int64_hash (gconstpointer v)
 
 /**
  * g_double_equal:
- * @v1: a pointer to a #gdouble key
- * @v2: a pointer to a #gdouble key to compare with @v1
+ * @v1: (not nullable): a pointer to a #gdouble key
+ * @v2: (not nullable): a pointer to a #gdouble key to compare with @v1
  *
  * Compares the two #gdouble values being pointed to and returns
  * %TRUE if they are equal.
@@ -2030,7 +2031,7 @@ g_double_equal (gconstpointer v1,
 
 /**
  * g_double_hash:
- * @v: a pointer to a #gdouble key
+ * @v: (not nullable): a pointer to a #gdouble key
  *
  * Converts a pointer to a #gdouble to a hash value.
  * It can be passed to g_hash_table_new() as the @hash_func parameter,