Replace ARPRequest/Reply with Pio::Arp::Request/Reply
Replace ICMP* classes with Pio::Icmp::Request/Reply.
Updated simple-router
Merge pull request #330 from shun159/feature/pio_arp_simple_router

Updated simple-router
Merge pull request #328 from trema/feature/pio_arp_simple_router

Replace ARPRequest/Reply with Pio::Arp::Request/Reply