Use match expression directly in guide.md

[jrincayc]

Use a match expression directly in the println statement, instead of creating a second variable. It seems weird that the current guide.md complains about creating an extra variable, when the same feature could be demonstrated without creating the extra variable.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @pcwalton (or someone else) soon.

[steveklabnik]

The point is to clearly show that the result of match is an expression, to be used however you see fit. I actually think that this is less clear.

[steveklabnik]

@aturon do we have any style guidelines here?

[huonw]

I agree that inlining the multiline match directly into the oneline println! is less clear, but it does seem like the complaint is strange: the temporary is "needed" for code clarity.

[jrincayc]

I agree that stylistically, putting the match directly inside the println! is somewhat ugly. I don't like how the documentation currently complains about doing an extra variable however, since the extra variable is unnecessary. (and for what it is worth, on O2, it looks like the compiler realizes that result is a constant and optimizes it away.)