Reorder imports (treat all 'extern create' as thirdparty)

[stanislav-tkach]

Motivation: we had a (not described formally) convention to separate usings into three groups: first thirdparty, then std and finally the internal ones. I propose to treat all external crate usings as thirdparty just because it is a formal criteria.

The order is discussable too.

[alekseysidorov]

What do you think about order such this?

use std;
use foreign_crates;
use exonum_crates;
use current_crate;

[aleksuss]

Let's be closer to community convention ?

use third_party_crates;

use std;

use current_crate;

pub use current_crate;

P.S. third_party_crates include exonum's crates as external dependencies

[stanislav-tkach]

I like this idea, especially because it seems that rust-fmt will probably enforce a similar order.

[stanislav-tkach]

Discussed, the following order should be used:

use std;
...

use extern_crate;
...

use inner;
...

pub use something;

Motivation: it is a popular ordering in other crates and in the rust-fmt RFC.
It can be convenient to separate our (exonum) extern crates from third-party crates, but such rule cannot be (easily) automated.

[aleksuss]

It'd be grate if you save this somewhere in a public place

[stanislav-tkach]

@aleksuss We have an issue (#109 and in JIRA too) for CONTRIBUTING.md/developer-notes.md.