https://www.jmeiners.com/lc3-vm/
https://www.jmeiners.com/lc3-vm/supplies/lc3-isa.pdf
https://www.rodrigoaraujo.me/posts/lets-build-an-lc-3-virtual-machine/

[x] opcode enum
[x] register getter/setter
[x] condition flags enum
[x] function to update the condition flags based on a register
[x] memory getter/setter
[x] read file as big-endian 2-byte instructions into memory
[x] fetch-execute loop
[x] implement execute
	[x] function: get opcode from instruction
	[x] match opcode to function
[x] implement opcodes
	[x] LEA
	[x] ADD (reg)
	[x] ADD (immediate)
	[x] AND (reg)
	[x] AND (immediate)
	[x] BR
	[x] JMP
	[x] JSR
	[x] JSRR
	[x] LD
	[x] LDI
	[x] LDR
	[x] LEA
	[x] NOT
	[x] RET
	[!] RTI
	[x] ST
	[x] STI
	[x] STR
	[x] TRAP (see jmeiners article)
		[x] getc
		[x] out
		[x] puts
		[x] in
		[x] putsp
		[x] halt
[x] keyboard mem-mapped i/o
	[x] KBSR
	[x] KBDR