Native review for BrianHicks/elm-benchmark

[BrianHicks]

The low level API for elm-benchmark is stable enough to review now. I'm still working on the high-level API.

Elm: https://github.com/BrianHicks/elm-benchmark/blob/master/src/Benchmark/LowLevel.elm
Native: https://github.com/BrianHicks/elm-benchmark/blob/master/src/Native/Benchmark.js

If it pleases the court, I'll submit a PR to the native whitelist.

Updates:

• 2017-02-20 (retroactive update on 2017-02-23): @eeue56 was kind enough to review the native code, I've made the improvements he suggested.
• 2017-02-23: I think the first version is ready to go. I'm going to go ahead and create a PR against native-whitelist.json

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[BrianHicks]

Closed with #222