[ANN] packetgen 2.1.3 released

packetgen 2.1.3 has been released.

* home: <https://github.com/sdaubert/packetgen>
* bugs: <https://github.com/sdaubert/packetgen/issues>
* doc: <https://github.com/sdaubert/packetgen/wiki>

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

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

Changes:

### 2.1.3 / 2017-11-01

* Add Types::Enum type. This new type is like Types::Integer but with a
limit set of values. All values are named.
** Update some headers to use it.
** Update Types::Fields to handle it.
* Update documentation:
** Update Dot11 documentation.
** add a wiki: https://github.com/sdaubert/packetgen/wiki.
* Add Utils module, adding some helper methods with ARP. Loaded by
default by pgconsole.
* Config class is now singleton.
handle packets on parsing.
* Add #calc_length to Header::RadioTap and Header::PPI.
* Some minor fixes:
** Fix PcapNG::UnknownBlock#to_s: body was set after block_len2.
** KISS PcapNG block types #to_s.
** Header::Dot11#to_w: sendind packets was impossible due to legacy code.
** Update Header::RadioTap and Header::PPI #parse? methods to better.