Improve CI

[lovasoa]

• Allow warnings on rust nightly (this allows keeping compatibility with both rust 1.20 and nightly)
• Create and independent script for CI instead of writing code inside .travis.yml
• Fix warnings in the tests

Fixes #327

[seanmonstar]

I think this means that when that lint makes it to beta (in a couple days?), we'll see it triggered there as well.

How about instead of removing the deny(warnings) entirely, just adding an allow where a warning we can't fix it triggered. Like:

#[allow(warnings)]
type AnyMap = HashMap<TypeId, Box<Any + Send + Sync>, BuildHasherDefault<IdHasher>>;

[lovasoa]

How about instead of removing the deny(warnings) entirely, just adding an allow where a warning we can't fix it triggered.

#[allow(warnings)] would allow any kind of warning on the portion of code it is applied to, not just compatibility warnings. Is that really what we want ?

I think this means that when that lint makes it to beta (in a couple days?), we'll see it triggered there as well.

Maybe warnings should be forbidden only on stable, then ?

[lovasoa]

on a side note: another change that this PR introduces is that warnings are disallowed even in tests.

[seanmonstar]

would allow any kind of warning on the portion of code it is applied to, not just compatibility warnings. Is that really what we want ?

Yep, that's fine. It's a smaller change, and there's no concern of other warnings being triggered.

[lovasoa]

Feel free to close or edit this PR if you think it is not relevant, then.