Improve support for binding pattern

Including improvements for parameters, variable assignment and
catch parameter.

lib/ast.js

@@ -989,7 +989,8 @@ var AST_ObjectProperty = DEFNODE("ObjectProperty", "key value", {
     $documentation: "Base class for literal object properties",
     $propdoc: {
         key: "[string|AST_Node] the property name converted to a string for ObjectKeyVal. For setters, getters and computed property this is an arbitrary AST_Node",
-        value: "[AST_Node] property value. For setters and getters this is an AST_Function."
+        value: "[AST_Node] property value. For setters and getters this is an AST_Function.",
+        default: "[AST_Expression] The default for this parameter, only used when nested inside a binding pattern"
     },
     _walk: function(visitor) {
         return visitor._visit(this, function(){