Update coding standards

Mentioned PHP versions indicate that there is a progress to make code
fully follow the coding standards which is not exactly the real case.
This patch changes few oudated used PHP versions in intro paragraph
and mentions the PHP documentation repository in more abstract way.

[ci skip]

CODING_STANDARDS

@@ -4,10 +4,9 @@
 
 This file lists several standards that any programmer adding or changing
 code in PHP should follow.  Since this file was added at a very late
-stage of the development of PHP v3.0, the code base does not (yet) fully
-follow it, but it's going in that general direction.  Since we are now
-well into version 5 releases, many sections have been recoded to use
-these rules.
+stage of the development of PHP v3.0, the code base does not fully
+follow it, but new features are going in that general direction.  Many
+sections have been recoded to use these rules.
 
 Code Implementation
 -------------------
@@ -298,5 +297,6 @@ highlight_file and show_source), will be separately documented. The
 proto should still be included, describing which function is aliased.
 
 Backwards compatible functions and names should be maintained as long
-as the code can be reasonably be kept as part of the codebase. See
-/phpdoc/README for more information on documentation.
+as the code can be reasonably be kept as part of the codebase. See the
+README in the PHP documentation repository for more information on
+documentation.