Add a customize mode where keys and options may be browsed and changed,

includes adding a brief description of each option. Bound to "C" by
default.

cmd-show-messages.c

@@ -18,6 +18,7 @@
 
 #include <sys/types.h>
 
+#include <stdlib.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
@@ -29,6 +30,9 @@
  * Show client message log.
  */
 
+#define SHOW_MESSAGES_TEMPLATE \
+	"#{t/p:message_time}: #{message_text}"
+
 static enum cmd_retval	cmd_show_messages_exec(struct cmd *,
 			    struct cmdq_item *);