Emit a 'raw' event for all raw buffers (in addition to per-packet-type)

With https://github.com/andrewrk/node-minecraft-protocol/pull/72 my use case was receiving all raw packet data so it could be proxied as-is, but https://github.com/andrewrk/node-minecraft-protocol/pull/80 added a new event type for each packet type:

       self.emit('raw.' + packetName, parsed.buffer);

which is makes this task difficult (would have to iterate each packet type, add listeners for each, unless I'm missing something…). So with this PR I added a bare 'raw' event, which is emitted for all packets regardless of their type:

       self.emit('raw', parsed.buffer);