Remove parens from nullary tag constructors in docs

Author: brson

doc/rust.texi

@@ -1990,22 +1990,22 @@ module system).
 An example of a @code{tag} item and its use:
 @example
 tag animal @{
-  dog();
-  cat();
+  dog;
+  cat;
 @}
 
-let animal a = dog();
-a = cat();
+let animal a = dog;
+a = cat;
 @end example
 
 An example of a @emph{recursive} @code{tag} item and its use:
 @example
 tag list[T] @{
-  nil();
+  nil;
   cons(T, @@list[T]);
 @}
 
-let list[int] a = cons(7, cons(13, nil()));
+let list[int] a = cons(7, cons(13, nil));
 @end example
 
 
@@ -3401,9 +3401,9 @@ control enters the block.
 An example of a pattern @code{alt} statement:
 
 @example
-type list[X] = tag(nil(), cons(X, @@list[X]));
+type list[X] = tag(nil, cons(X, @@list[X]));
 
-let list[int] x = cons(10, cons(11, nil()));
+let list[int] x = cons(10, cons(11, nil));
 
 alt (x) @{
     case (cons(a, cons(b, _))) @{