[Reverse String]: Add Approaches, Performance, and Unicode Articles

[BethanyG]

Added an Introduction.md and the Following Approaches:

1. Sequence Slice with Negative Step
2. Iteration with String Concatenation
3. Reverse Iteration with Range()
4. Make a list and Use str.join()
5. Make a list and use list.reverse()
6. Use the built-in reversed()
7. Other interesting approaches

Also added:

• Performance article,
• Benchmark code
• An article about working with Unicode strings outside of the ASCII range in Python (STUBBED currently)

[colinleach]

This is remarkably good for something so long and complicated. I can see why it stressed you out for so long!

You already fixed the 2 minor things I found. I didn't see anything to comment on otherwise, and I think I've now read all of it.

Good luck with the Unicode article. I can't help you with that.

[BethanyG]

Good luck with the Unicode article. I can't help you with that.

I am going to finish the Raindrops approaches (which aren't as good as these) and review Roman Numerals before looping back to this. You deserve to have your work merged, and it would be nice to hit the Raindrop deadline.

Thank you so much for giving this a review. It is such a relief to know that it wasn't absolutely bonkers. I am very happy that its good if long-winded & complicated. 😄