RET didn't decrement the stack pointer resulting in unintended overflows.

Turns out there _was_ a reason the program was overflowing and it was my fault.

src/main.rs

@@ -48,6 +48,9 @@ impl Cpu {
 	fn incrementsp(&mut self) {
 		self.sp = self.sp + 1
 	}
+	fn decrementsp(&mut self) {
+		self.sp = self.sp - 1
+	}
 	fn stackpush(&mut self) {
 		if self.stack.len() == 15 {
 			println!("Stack overflow in emulated CPU! Bailing out!");
@@ -248,6 +251,7 @@ fn execute(opcode: u16, instruction: Instruction, mut cpu: Cpu) -> Cpu {
 
 	if instruction.name == "RET" {
 		let returnaddress = cpu.stackpop();
+		cpu.decrementsp();
 		cpu.setpc(returnaddress);
 	}
 	else if instruction.name == "JP_ADDR" { cpu.setpc(args[0] as u16); }