Update autoconf initialization

Require a more recent autoconf, and name the dist archive vmod-example
to match the usual package naming scheme. Update the copyright notice.

configure.ac

-AC_PREREQ(2.59)
-AC_COPYRIGHT([Copyright (c) 2011-2015 Varnish Software AS])
-AC_INIT([libvmod-example], [0.1])
+AC_PREREQ([2.68])
+AC_INIT([libvmod-example], [0.1], [], [vmod-example])
+AC_COPYRIGHT([Copyright (c) 2011-2016 Varnish Software AS])
 AC_CONFIG_MACRO_DIR([m4])
 m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))
 AC_CONFIG_SRCDIR(src/vmod_example.vcc)