Split function and operator User Guide info

 from datatype.sgml into separate files.
Add type conversion information.
Format historical release notes.

doc/src/sgml/docguide.sgml

@@ -239,7 +239,7 @@ right, and I can verify the document with "nsgmls -s docguide.sgml".
 <title>Building Documentation</title>
 
 <para>
-GNU <programname>make</programname> is used to build documentation from the DocBook sources.
+GNU <application>make</application> is used to build documentation from the DocBook sources.
 There are a few environment definitions which may need to be set or modified for your installation.
 The <filename>Makefile</filename> looks for 
 <filename>doc/../src/Makefile</filename>

doc/src/sgml/postgres.sgml

@@ -18,6 +18,9 @@
 <!entity environ  SYSTEM "environ.sgml">
 <!entity manage   SYSTEM "manage.sgml">
 <!entity datatype SYSTEM "datatype.sgml">
+<!entity oper     SYSTEM "oper.sgml">
+<!entity func     SYSTEM "func.sgml">
+<!entity typeconv SYSTEM "typeconv.sgml">
 <!entity array    SYSTEM "array.sgml">
 <!entity inherit  SYSTEM "inherit.sgml">
 <!entity query-ug SYSTEM "query-ug.sgml">
@@ -162,6 +165,9 @@ Information for users.
 &environ;
 &manage;
 &datatype;
+&oper;
+&func;
+&typeconv;
 &array;
 &inherit;
 &query-ug;

doc/src/sgml/user.sgml

@@ -11,6 +11,9 @@
 <!entity environ  SYSTEM "environ.sgml">
 <!entity manage   SYSTEM "manage.sgml">
 <!entity datatype SYSTEM "datatype.sgml">
+<!entity oper     SYSTEM "oper.sgml">
+<!entity func     SYSTEM "func.sgml">
+<!entity typeconv SYSTEM "typeconv.sgml">
 <!entity array    SYSTEM "array.sgml">
 <!entity inherit  SYSTEM "inherit.sgml">
 <!entity query-ug SYSTEM "query-ug.sgml">
@@ -92,6 +95,9 @@ It provides SQL92/SQL3 language support,
 &environ;
 &manage;
 &datatype;
+&oper;
+&func;
+&typeconv;
 &array;
 &inherit;
 &query-ug;