Add InPacket interface and ByteBuf implementation

Replacement for LittleEndianAccessor, SeekableLittleEndianAccessor,
GenericLittleEndianAccessor, and GenericSeekableLittleEndianAccessor.

src/main/java/net/packet/Packet.java

@@ -0,0 +1,5 @@
+package net.packet;
+
+public interface Packet {
+    byte[] getBytes();
+}