[ANN] packetgen 3.1.5 released

packetgen 3.1.5 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.

Supported protocols are: Ethernet, Dot11, Dot1x, ARP, IP, IPv6, GRE,
ICMP, IGMP, ICMPv6, MLD, MLDv2, OSPFv2, OSPFv3, UDP, TCP, SNMP, DNS,
EAP, BOOTP, DHCP, TFTP, HTTP and MDNS.

Changes:

### 3.1.5 / 2020-03-31

* Add support for setting monitor mode when capturing packets (optix2000).
* Add PacketGen.loopback_iface to get loopback interface.
* Add Types::fields.bit_fields to get bit field definitions for given class.
* Add Inspectable module to share methods to format types when
inspecting headers.
* Refactor and clean up code.
* Bugs:
    * Fix Utils.arp: really use iface information.
    * Fix string interpolation in Types::AbstractTLV#to_human (optix2000).
    * Fix Deprecation.deprecated and Deprecation.deprecated_class in
some obsure cases (optix2000).