Bump version and add version notes.

kcgi.h

@@ -53,7 +53,7 @@
 /*
  * Build version.
  */
-#define	KCGI_VBUILD	2
+#define	KCGI_VBUILD	3
 
 /*
  * Version string of major.minor.build (as a literal string).

versions.xml

@@ -1,6 +1,20 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <!-- vim: set tw=100: -->
 <articles>
+	<article data-sblg-article="1" data-sblg-tags="version">
+		<header>
+			<h1>0.12.3</h1>
+			<address>Kristaps Dzonsons</address>
+			<time datetime="2021-01-20">2021-01-20</time>
+		</header>
+		<aside>
+			<div>
+				<b>Bug fix</b>: fix some bad pointer arithmetic on a regression test
+				on Linux.  While here, fix how <code>make regress</code> would spam
+				some systems with erroneous warning messages.
+			</div>
+		</aside>
+	</article>
 	<article data-sblg-article="1" data-sblg-tags="version">
 		<header>
 			<h1>0.12.2</h1>