mal-dns2bro.sh: add helper script for Bro's Intel Framework

Mal-dns2bro.sh is a helper script to be used with mal-dnssearch
that outputs reputation list in a format suitable for the Intel
Framework in Bro 2.2.

It can read from a file or accepts stdin and can make a few modific-
ations to the intel data like Intel::Type and other records such as
meta.source, meta.do_notice, and meta.if_in.

Once mal-dns2bro receives the parsed list from mal-dnssearch it will
make each record of Intel::DOMAIN and specify a string for the intel
source, other options are available.

e.g. ``mal-dnssearch -M mandiant -p | mal-dns2bro -T dns -s mandiant''