add `npm run profile`.

* This should open up a new window (ideally Chrome).
* Pop open the Dev Tools. Click on the Profile tab.
* Hit escape to view the console as well.
* Once the profile "all" is complete, you should be able to inspect the run.

Of note: V8 has a sampling profiler -- so if the stacks look a bit odd, it's usually
because the sampling caught at a weird moment. By default the benchmark is configured
to run each of:

1. Large: Unminified, concatenated JSHint codebase.
2. Medium: Unminified, concatenated jQuery 2.1.0 codebase.
3. Small: Unminified, concatenated Knockout codebase.
move to tests/bench
Merge pull request #591 from chrisdickinson/add-benchmarks

add `npm run profile`.