Apply clippy suggestions

[gnieto]

I've ran clippy on the project and it reports some issues. I think it would be nice to apply the suggestions and even ran clippy on CI/Travis.

What do you think?

[sunchao]

+1. I think this will be a good thing to add.

[sadikovi]

Can you be clear if those are issues or suggestions?

[sadikovi]

I just ran it, it reports a bunch of warnings and errors, and a lot of them are false positives. I am not sure we want to do it automatically on every build, but doing it once to fix some of the issues could be beneficial, similar to what we did with style. Cheers!