patch 9.1.0564: id() can be faster

Problem:  id() can be made faster
Solution: don't use printf(), use clever shift of pointer
          (Ernie Rael)

closes: #15207

Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 96d774e..b25bb93 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -309,7 +309,7 @@
 hlset({list})			Number	set highlight group attributes
 hostname()			String	name of the machine Vim is running on
 iconv({expr}, {from}, {to})	String	convert encoding of {expr}
-id({item})			String	get address of item as a string
+id({item})			String	get unique identity string of item
 indent({lnum})			Number	indent of line {lnum}
 index({object}, {expr} [, {start} [, {ic}]])
 				Number	index in {object} where {expr} appears