Thread-safe (lock-free) maps

[kirillDanshin]

We want to get rid from using mutex when working with maps.
We need to fix concurrent read/write in maps.
To do that we need to remove throws about concurrent write/read-write, fix growWork and evacuate() and write as many as possible tests for maps.

• basic implementation
• tests

[bcmills]

See also golang/go#18177.

[kirillDanshin]

@bcmills thanks. glad to see that Golang team is working on this.
notice, that this issue is about replacing maps to its thread-safe and lock-free implementation, so it's not about adding something, it's about fixing original implementation while saving backward compatibility.
but, as you can see here, Go will not support thread-safe lock-free map implementation. but I'll do.

[kirillDanshin]

also, about the status of this issue. now I'm testing it in my stage and production environments, there's no data corruptions, no panics etc, so I think it's ready.

upd: when I'm done with testing, I'll push the implementation, and I should write some tests (about 50-100 should be enough).