Support rust 1.19

[Undin]

Rust 1.19 is released 🎉🎉🎉.

So I think we should support next features:

• CI builds with rust 1.19
• numeric fields for tuple structs
• unions
• loop expressions
• eprint! and eprintln! macros

[farodin91]

eprint! and eprintln! should work. You can auto complete them.

[Undin]

Yes, auto completion and type inference should work at this moment. But we can know a little bit more about structure of these elements that can be useful in some other plugin features, for instance, #1490

[farodin91]

rust-lang/rfcs#1506

[Undin]

Oh, it's the first feature of this release I've known.
I've forgotten about it.
Thanks a lot!