Fix FX0A GET KEY

[guilherme-puida]

The test rom describes the following behavior:

Fx0A waits for a key press and returns the pressed key in vX.

The test asks you to press a key on the CHIP-8 keypad. When you do, it checks for two issues that are easy to accidentally introduce when implementing this opcode. If all is well, you should be seeing a checkmark and "all good" on the screen:

Otherwise, you can get either of these errors:

NOT HALTING - Your implementation immediately returns the value of any currently pressed keys in vX, instead of halting the interpreter until a key is pressed (note that this needs timer support to be accurate)
NOT RELEASED - Your implementation doesn't wait for the pressed key to be released before resuming

See this article for more information.

The current output is x not released, when it should be ✓ all good.