Implement date and time getting/setting

[RandomInsano]

The date setting works just fine. The time, not so much. I assume this is because I'm using DOSBox for development, but I'm honestly not sure.

References:

• http://spike.scu.edu.au/~barry/interrupts.html
• https://www.cs.uaf.edu/2017/fall/cs301/lecture/09_11_registers.html