This updates the packet header so that the encryption byte flag is now
32 bits. This also updates the powershell and python extensions so that
both of the bindings work correctly as a result of the TLV packet header
changes.
Make the XOR key an array of bytes as a start to normalise the way the
XOR happens across the board. Given that we're going to be adding
encryption to the packet level and adding more stuff to the packet
header, now is the time to fix this up once and for all.