bump version, update NEWS

NEWS

+Knot DNS 1.6.7 (2016-02-08)
+===========================
+
+Improvements:
+-------------
+- IXFR: Log change of the zone serial number after the transfer.
+- RRL: Document operational impact of various settings.
+- RRL: Add support for zero slip (dropping of all limited responses).
+
 Knot DNS 1.6.6 (2015-11-24)
 ===========================
 

configure.ac

 #                                               -*- Autoconf -*-
 
 AC_PREREQ([2.60])
-AC_INIT([knot], [1.6.6], [knot-dns@labs.nic.cz])
+AC_INIT([knot], [1.6.7], [knot-dns@labs.nic.cz])
 AM_INIT_AUTOMAKE([gnits subdir-objects dist-xz -Wall -Werror])
 AM_SILENT_RULES([yes])
 AC_CONFIG_SRCDIR([src/knot/main.c])