QUIC Support.

I am aware support for protocols in the layers package are on a per-packet basis, and stream based protocols should be focused on reassembly rather than decoding.

I wanted to raise the idea of decoding QUIC packets on top of UDP, in the same manner as TLS on TCP.

I have a minimal layers package for QUIC somewhat written at this point, and I would be happy to contribute that code directly to the gopacket repository if the maintainers feel it would be worth contributing.