16 bit registers in register message are being trucated

[jkleve]

The register message is currently only set up to be able to send 8 bits. This is truncating the top 8 bits. Suggest making this a more generic message where we are sending a memory address and size.

[jkleve]

It is also the address of the register that can get truncated. Ran into the issue when implementing timer 5 which has its counter at address 0x124. Made register message 4 bytes instead of 2. Made data and word messages a separate message type.