Replace try! with question mark operator

[yoshinorisano]

There are a lot of compiler warnings when building hound:

warning: use of deprecated macro `try`: use the `?` operator instead

So I tried to fix that. Does this make sense to you?

[yoshinorisano]

@ruuda Hi! Could you review this?

[atoktoto]

It would be great if this got merged. I'm working on a no_std support for this library. While I don't expect my changes will ever get merged (I had to switch to nightly) having this accepted would make it easier for me to keep my fork in sync with future changes.

[maxtimbo]

@ruuda Can this be merged?