Rust-clippy: Run Clippy over various crates in new travis build

[phansch]

It would be nice to have a way to run clippy over a bigger rust codebase than just our tests on Travis/AppVeyor.
We could start by running Clippy over a couple of crates in a separate CI job and ensure that cargo clippy does not cause an ICE in any of the crates.

This would also allow us to detect breaking changes inside clippy before we do a release.

To close this issue, the following crates should be checked:

Crates to include:

• [x] futures-rs
• [x] rand
• [x] failure
• [x] rustfmt
• [x] log
• [x] chalk
• [x] nom
• [x] stdsimd
• [x] cargo
• [x] serde
• [x] chrono

[oli-obk]

crates like serde do not trigger any clippy lints, so we can even check those for new lint occurrences.

We should probably start this out as a travis job that is allowed to fail.

[phansch]

rustfmt is also doing something similar now: https://github.com/rust-lang-nursery/rustfmt/issues/2692

[matthiaskrgr]

At cppcheck we run cppcheck on all of the debian package sources and save the output and summarize the results:
http://cppcheck.sourceforge.net/devinfo/daca2-report/daca2.html

https://github.com/danmar/cppcheck/tree/master/tools (the daca files)

Maybe something similar could be done for clippy with the crater test set?
EDIT: (not during ci, but maybe continuosly on some other computer (cppcheck "daca" was runnning off a RPI for several months for example)