Strings chapter again (and again)

[CGMossa]

Somehow, this chapter got deleted.

I don't think it flows at all and could use some heavy suggestions.. But here it is!

[kbvernon]

A couple of suggestions here:

1. Add an introduction that briefly explains what the reader can expect to get out of this article.
2. Demonstrate the challenges of working with character strings in the R+Rust context using some examples involving Rust and extendr types - String, Rstr, Strings, Vec<String> - and show some common errors that you think are likely to come up.
3. Include references to The Book: https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html and https://doc.rust-lang.org/book/ch08-02-strings.html. If you think there are other sources that could be helpful, include those, too.