Changes to the LEA and TRAP instructions in the Third Edition about lc3-vm

[rpendleton]

Similar to #51, I'm not sure what the best move is here.

I searched around online a bit, but only found official online resources for the second edition of the book. I wasn't able to find an official simulator or public copy of Appendix A for the third edition of the book. Also, the third-party simulators I found seemed to also follow the second edition spec.

On the one hand, I can understand wanting to keep this tutorial and its implementation up-to-date with the latest edition of the book LC-3 is defined by. However, since that edition isn't as common online, it makes me wonder if it would be better for us to just call out that the guide is based on the second edition of the book, and that later editions may vary.

[auraes]

Yeah, you're the one who knew what's best.

[rpendleton]

After some discussion, we've decided to continue implementing the LC-3 architecture as defined by the second edition of the textbook, primarily due to the more widespread availability of second edition resources. I've updated the tutorial to indicate that we're using the second edition in 403778f.

Thanks for calling out the difference though!