std.benchmark is in reviewable state

[Andrei Alexandrescu]

I've had a good time with std.benchmark today and made it ready for 
submission to Phobos. As a perk I've added the %h format specifier, 
which formats a number in human-readable form using SI prefixes.

For those interested in discussing this prior to the formal review 
process, the code is at:

https://github.com/andralex/phobos/blob/benchmark/std/benchmark.d
https://github.com/andralex/phobos/blob/benchmark/std/format.d

and the dox at

http://erdani.com/d/web/phobos-prerelease/std_benchmark.html
http://erdani.com/d/web/phobos-prerelease/std_format.html

Comments and suggestions are welcome. If possible, it would be great if 
this submission were given a bump in the priority queue. This is because 
with robust benchmarking in Phobos we can ask new, performance-sensitive 
submissions, to add benchmarking.


Thanks,

Andrei