[glib] gclosure: Expand documentation and fix some typos

[Philip Withnall <pwithnall src gnome org>]

commit 16e58dc901c8951d8eeb20efa8e78ba9ae96723c
Author: Philip Withnall <withnall endlessm com>
Date:   Thu Apr 26 18:04:47 2018 +0100

    gclosure: Expand documentation and fix some typos
    
    The critical omission from the GClosure documentation is that you need
    to call g_closure_set_marshal() when implementing a custom GClosure.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    Reviewed-by: nobody

 gobject/gclosure.c | 4 +++-
 gobject/gclosure.h | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gobject/gclosure.c b/gobject/gclosure.c
index caa11549c..b42af60bb 100644
--- a/gobject/gclosure.c
+++ b/gobject/gclosure.c
@@ -54,7 +54,9 @@
  * library provides the #GCClosure type for this purpose. Bindings for
  * other languages need marshallers which convert between #GValues
  * and suitable representations in the runtime of the language in
- * order to use functions written in that languages as callbacks.
+ * order to use functions written in that language as callbacks. Use
+ * g_closure_set_marshal() to set the marshaller on such a custom
+ * closure implementation.
  *
  * Within GObject, closures play an important role in the
  * implementation of signals. When a signal is registered, the
diff --git a/gobject/gclosure.h b/gobject/gclosure.h
index 393348c7c..a5c1c3fcb 100644
--- a/gobject/gclosure.h
+++ b/gobject/gclosure.h
@@ -200,7 +200,7 @@ struct _GClosure
 
   /*< private >*/      GClosureNotifyData *notifiers;
 
-  /* invariants/constrains:
+  /* invariants/constraints:
    * - ->marshal and ->data are _invalid_ as soon as ->is_invalid==TRUE
    * - invocation of all inotifiers occours prior to fnotifiers
    * - order of inotifiers is random