Add support for udp6 multicast

[jedahan]

So this is my first attempt at supporting udp6 multicast for broadcast-stream.

It is off by default, and uses ff02::114 but you can override that.

I also added a lua dissector for wireshark as a useful utility, but maybe that should be in a subfolder like util/ or contrib/ ?

Would love to get your feedback. Cheers!

[jedahan]

FYI this is not ready to merge

[dominictarr]

please don't put any thing ssb specific in this module, but happy to add links to things. also keep it es5 (so no destructuring please). let me know when it's ready