Merge pull request #9 from kylemcdonald/master

Allow Sniffer to enable monitor mode on interface
Merge pull request #11 from kylemcdonald/master

changed ICMP::check to ICMP::checksum
Simplified error string generation on Sniffer::pcap_open_live_extended.
Fixed compilation error in RSNInformation.
Fixed compilation errors on Windows.
Added small option optimization to PDUOption.
Added method in TCP and IP that emplaces an option.
Fixed ICMPv6 checksum calculation.
Added call to pcap_can_set_rfmon before calling pcap_set_rfmon.
Added check for HAVE_DOT11 macro in RSNInformation header/source files.
Added undef directive to avoid compilation error on windows.
Fixed error compilations on windows.
Updated example.
Updated copyright notice.
added Utils::to_string(PDU::PDUType). closes #12.