Merge tag '0.4.0' into develop

0.4.0
Add CHANGELOG.md etc. to gem.
Add OpenFlow Hello message generator and parser (refs #57).
Deleted an unused file.
Merge pull request #58 from shun159/deleted_an_unused_file

Deleted an unused file(refs #56).
Delete the `dhcp_' prefix since it is redundant
Merge pull request #59 from shun159/delete_the_`dhcp_`_prefix_since_it_is_redundant

Delete the `dhcp_' prefix since it is redundant(refs #56)
Merge remote-tracking branch 'origin/develop' into develop
Add cucumber task (refs #20).
Add a scenario that tests Pio::Arp.read (refs #20).
Add cucumber profiles.
Add cucumber files to gem.
Merge pull request #61 from trema/feature/cucumber_pcap

Feature/cucumber pcap
New pcap: arp-storm.pcap (refs #62).
Add cucumber guard (refs #62).
New pcap: icmp.pcap (refs #62).
New pcap: lldp.minimal.pcap (refs #62).
New pcap: lldp.detailed.pcap (refs #62).
Add `dump_pcap' rake task (closes #20).

Usage: rake PCAP='icmp.pcap' dump_pcap
Add `dump_pcap' rake task.