Fixes random access to Tx buffer - wasn't taking in to account control byte at start of buffer.
Add GetChecksum function which uses ENC28J60 built in checksum generator.
TxAppend now returns value indicating success.
Use transaction for PacketSend helper function.
Add test case for large Tx Packets (not currently working - wip).
Fixes bug with TxWrite failing due to writing byte rather than word to register.
Re-orgnaise memory structure.
Fix DMACopy routine - not yet tested.
Rename Htons to SwapBytes.