Add SystemVerilog Support

[jwrr]

SystemVerilog has added a do-while loop, so 'do' is now a reserved word. The TV80's Data Output bus is named 'do' which causes a compilation error when using icarus -g2012 (systemverilog partial support). I'm using cocotb for testing and it uses the -g2012 switch.

I have created a branch that changes 'do' to 'data_output'. To keep consistent naming I also changed 'di' to 'data_in'. If you're interested, I have created a pull request. Best Regards.

ps: with these changes, the simulation runs well in cocotb.

[abnoname]

thanks :-)