Move Ownership Part 2 content into Part 1

[jespiron]

In #50

Any chance we can move this lecture 5 content to lecture 2?

The parts I like are

• Quick TL;DR of stack and heap, with diagrams. Lecture 2 speaks as though students are already familiar with the stack and heap, and then we throw around the words "stack" and "heap" some more in lecture 4 collections and generics. It makes sense to equip them with this foundational info in lecture 2
• Diagrams really illustrate that deep-copying is expensive!! + good motivation for references. We can put the animations in this section of Part 1
• My Part 2's wording of "Inspired by the stack! Sound familiar? Let's apply these rules to the heap" communicates the same message as Part 1's "What if we tied memory allocation to the scope of a variable?", except it walks through the extremely abstract sentence "tie memory allocation to the scope of a variable" with something tangible. Students can see "omg the stack rules rhyme with ownership rules!"
• My Q&A of "Pretend you're the compiler, marking out places to deallocate heap memory...when is it safe and how do you know it's safe?"
• My wording of "C's proposal: leave it to the programmer, Java's proposal: leave it to runtime, Rust's proposal: prevent at compilation time" can be incorporated in this section of Part 1. This gives students an easy-to-remember tagline when they're asked to compare Rust with other languages.
  I expect "What's the difference between a garbage collector and Rust's borrow checker?" to be a common question, since we open lecture 2 with "no garbage collector!!" This was definitely a question I had before I learned Rust. By saying "leave it to runtime / prevent at compilation" this clarifies that the difference is when the solution occurs.
• In lecture 2, we throw around the word "undefined behavior" without defining it. Addressing it even briefly would be nice

Even a subset of the above suggestions is good! I recognize this makes the first half of lecture 5 redundant, in which I'm willing to rewrite lecture 5.

I think these changes are worth the effort, since it makes Lecture 2 intuitive while giving us more avenue for lecture 5 content.

[connortsui20]

I don't know how much time you have, but if you could make a PR to lecture 2 showing high level changes (you don't have to write out entire slides, just add titles and a brief description of what the slide shows) I think it would make making a decision easier.

Lecture 2 is already packed with information, and is also one of the lecture that tends to go over. The goal of having the new Ownership (Part 2) lecture was to take information out of lecture 2 and move it somewhere else, so I am super hesitant to move more stuff into lecture 2.

I'm sure adding this stuff is a good idea, but we also need to make sure students can do the homework. I don't know exactly which of these variables need to change, so if you have time to make a draft PR to lecture 2 that would be great.

[jespiron]

The timing is indeed difficult.

After playing around with this, I decided Part 1 is sufficiently explained.

I opted for a smaller change, of rearranging and trimming: #52