Add complete support for std lib macros such as println!

[Dushistov]

Thanks for your tool,

I think it would be nice to complete for polular macros from std:

println!, unimplemented!, unreachable!, assert!, assert_eq!

[mqudsi]

I would add eprintln to the list, it probably wasn't around when this issue was created.

I feel the lack of support for these macros should be a blocker as the first thing someone will want to do to try out racer is cargo init --bin and play with the single line of code that generates: println!(....).

[BatmanAoD]

Also vec!.

[julitopower]

Is there any work being done for this?

[kngwyu]

@julitopower
No, but I'm planning to add partial macro support(only for stdlib macros) before 2.1

[kngwyu]

Closed via #902