Implement a new system-based matching harness.

The intent is to look for platform-specific facilities for regex
matching, to provide portable MENUCOLORS configuration files.

This is a prototype implementation being committed to see if Windows can
use the POSIX regex implementation provided with the C++11 standard
library. If this works, I will write a harness for POSIX regexes and for
pmatch(), and those can be linked in by platforms as appropriate.

pmatch() should be used only as a very last resort, because it breaks
compatibility between platforms.

include/nhregex.h

@@ -0,0 +1,19 @@
+/* NetHack 3.5	nhregex.h	$NHDT-Date: 1428084467 2015/04/03 18:07:47 $  $NHDT-Branch: scshunt-regex $:$NHDT-Revision: 1.0 $ */
+/* NetHack 3.5	nhregex.h	$Date: 2009/05/06 10:44:33 $  $Revision: 1.4 $ */
+/* Copyright (c) Sean Hunt  2015.                                 */
+/* NetHack may be freely redistributed.  See license for details. */
+
+#ifndef NHREGEX_H
+#define NHREGEX_H
+
+#include <hack.h>
+
+struct nhregex;
+
+struct nhregex *regex_init(void);
+boolean regex_compile(const char *s, struct nhregex *re);
+const char *regex_error_desc(struct nhregex *re);
+boolean regex_match(const char *s, struct nhregex *re);
+void regex_free(struct nhregex *re);
+
+#endif