new functions ecalloc() and die()

die() replaces EBARF and BARF
and allow us to add `-pedantic` to CFLAGS

util.h

@@ -0,0 +1,4 @@
+/* See LICENSE.dwm file for copyright and license details. */
+
+void die(const char *fmt, ...);
+void *ecalloc(size_t nmemb, size_t size);