Option to skip uneccessary match arm brackets

[TheBlueMatt]

If rustfmt decides to indent after the => in a match (because the line ran too long) it also adds a {} and an extra line (for the }) even if the contents of the match arm fit onto a single line.

In the example at rust-bitcoin/rust-bitcoin#959 (comment) rustfmt generated

Error::SerializationError => {
    "can not serialize the spending transaction in Transaction::verify()"
},

when it arguably could have (optionally) just stuck with

Error::SerializationError =>
    "can not serialize the spending transaction in Transaction::verify()",

unlike ifs (and the C world) you can't get screwed by the lack of {} here - if you end up with two statements back-to-back its a compile error rather than incorrect logic.

Thanks!

[calebcartwright]

Thanks for sharing, but going to close as a duplicate of #4896

You may want to also subscribe to #4924. It may have stalled out a bit but made good progress and is the most likely candidate for implementation