add Packet class

ackhandler/packet.go

@@ -0,0 +1,12 @@
+package ackhandler
+
+import "github.com/lucas-clemente/quic-go/protocol"
+
+// A Packet is a packet
+type Packet struct {
+	PacketNumber protocol.PacketNumber
+	Plaintext    []byte
+	EntropyBit   bool
+
+	MissingReports uint8
+}