added btime and belapsed macros, fixed prettymemory to use SI units

[stevengj]

This PR adds two macros, @btime and @belapsed, that are drop-in replacements for @time and @elapsed from Base except that they use the @benchmark apparatus. For example:

julia> @btime sin(1)
  11.410 ns (0 allocations: 0 bytes)
0.8414709848078965
 
julia> @belapsed sin(1)
1.1412412412412412e-8

It also changes the memory output to use SI prefixes. Previously, it would output something like 17.34 kb, which is ambiguous — is a kb 1000 or 1024 bytes (we use 1024)? The SI ISQ prefix is "KiB" for kibibyte, which unambiguously means 1024 bytes.

Also, it now prints 24 bytes and not 24.00 bytes — the decimal point was confusing since (presumably) we will never be able to allocate a fractional number of bytes.

Closes #35.

[stevengj]

Test failure in 0.6 is due to #38.

[jrevels]

Why is this getting done twice here?

[stevengj]

Typo, sorry

[stevengj]

Yay, tests are passing in the rebased branch.

[stevengj]

Rebased.

[jrevels]

Thanks!

[stevengj]

See also JuliaLang/julia#20173

[KristofferC]

@btime is awesome and something that I have wanted for a long time (without realizing it).

[tkelman]

what is this using from 0.9.5?

[stevengj]

I can't remember, maybe it was the Symbol constructor? I definitely upgraded the Compat requirement for a reason.

[tkelman]

Symbol is older I believe - probably JuliaLang/Compat.jl@2c11855

Maybe an earlier version of this was using one of the show rewrites? doesn't look like the final version is though

[stevengj]

I think maybe an earlier version tried to use a buffer and String(take!(buf)) for the @btime test, which requires Compat 0.9.5. I then rewrote it to use redirect_stdout(f) with a temporary file, which requires Compat 0.9.0 (JuliaLang/Compat.jl@2c11855)