std.experimental.logger formal review round 3

[Dicebot via Digitalmars-d]

Previous review thread : 
http://forum.dlang.org/post/zhvmkbahrqtgkptdlcvh@forum.dlang.org

Previous voting thread (also contains discussion in the end) : 
http://forum.dlang.org/post/vbotavcclttrgvzcjjia@forum.dlang.org

Code : https://github.com/D-Programming-Language/phobos/pull/1500

Important changes since last review:
- new approach for compile-time log level filtering
- thread-safe API (by Marco Leise, commits 3b32618..e71f317)
- documentation enhancements all over the place
- more @nogc annotations
- "raw" log overload that expects pre-formatted message and all 
metadata (file/line/function) as run-time function arguments

(anything I have missed Robert?)

Usual process : 2 weeks for checking out if there are any 
critical issues that are likely to prevent successful voting, 
write a comment if you need more time for review, focus on API 
issues.