[ANN] packetgen 1.4.2 released

packetgen 1.4.2 has been released.

* home: <https://github.com/sdaubert/packetgen>
* bugs: <https://github.com/sdaubert/packetgen/issues>
* doc: <http://www.rubydoc.info/gems/packetgen>

PacketGen provides simple ways to generate, send and capture network
packets.

Known protocols are: Ethernet, Dot11, Dot1x, IP, IPv6, ARP, ICMP,
ICMPv6, UDP, TCP, ESP and DNS.

Changes:

### 1.4.2 / 2017-03-30

* add Types::Int#sz
* fix Types::Array#read to not grab all data in string but only bytes needed
* improve Types::Array:
** add .set_of to define type of objects handled by array
** add a default #record_from_hash method
** add a counter management as was in Header::DNS::RRsection
* fix Config#initialize: get hwaddr on Mac OS X systems