Add InPacket interface and ByteBuf implementation

Replacement for LittleEndianAccessor, SeekableLittleEndianAccessor,
GenericLittleEndianAccessor, and GenericSeekableLittleEndianAccessor.

src/main/java/net/packet/ByteBufOutPacket.java

@@ -0,0 +1,11 @@
+package net.packet;
+
+import io.netty.buffer.ByteBuf;
+
+public class ByteBufOutPacket implements OutPacket {
+    private final ByteBuf byteBuf;
+
+    public ByteBufOutPacket(ByteBuf byteBuf) {
+        this.byteBuf = byteBuf;
+    }
+}