Improve compatibility with older Rust versions

[b-r-u]

Previously, the lin module required Rust 1.22 or newer. It now
compiles with 1.14.

[soc]

@b-r-u I apologize for the delay, I was pretty busy sorting out some blockers for a 1.0 release :-/ ... this looks good to me!

Thanks!

[soc]

Can you add some context to your comment from the issue regarding

it looks like everything works even with 1.13 (from 2016-11-10, which stabilized the ? operator) with a minor change

... but in the above change you remove ? altogether. What's the story here?

[b-r-u]

The commit removes the ? operator because it was used on an Option (instead of a Result) and this was introduced in Rust 1.22 (https://blog.rust-lang.org/2017/11/22/Rust-1.22.html).

I was mentioning the introduction of the ? operator with Rust 1.13 because I think it was very much embraced by the community and there is limited benefit from supporting older Rust versions by now.

[soc]

@b-r-u Ah, thanks! Now I understood it.