Fix a reference to the MRE book in re docs (GH-1113)

Reported by Maksym Nikulyak on docs.p.o.

Doc/library/re.rst

@@ -67,8 +67,8 @@ string *pq* will match AB.  This holds unless *A* or *B* contain low precedence
 operations; boundary conditions between *A* and *B*; or have numbered group
 references.  Thus, complex expressions can easily be constructed from simpler
 primitive expressions like the ones described here.  For details of the theory
-and implementation of regular expressions, consult the Friedl book referenced
-above, or almost any textbook about compiler construction.
+and implementation of regular expressions, consult the Friedl book [Frie09]_,
+or almost any textbook about compiler construction.
 
 A brief explanation of the format of regular expressions follows.  For further
 information and a gentler presentation, consult the :ref:`regex-howto`.
@@ -492,14 +492,6 @@ three digits in length.
    The ``'\N{name}'`` escape sequence has been added. As in string literals,
    it expands to the named Unicode character (e.g. ``'\N{EM DASH}'``).
 
-.. seealso::
-
-   Mastering Regular Expressions
-      Book on regular expressions by Jeffrey Friedl, published by O'Reilly.  The
-      second edition of the book no longer covers Python at all, but the first
-      edition covered writing good regular expression patterns in great detail.
-
-
 
 .. _contents-of-module-re:
 
@@ -1585,3 +1577,9 @@ The tokenizer produces the following output::
     Token(typ='END', value=';', line=4, column=27)
     Token(typ='ENDIF', value='ENDIF', line=5, column=4)
     Token(typ='END', value=';', line=5, column=9)
+
+
+.. [Frie09] Friedl, Jeffrey. Mastering Regular Expressions. 3rd ed., O'Reilly
+   Media, 2009. The third edition of the book no longer covers Python at all,
+   but the first edition covered writing good regular expression patterns in
+   great detail.