Added Benchmark.js v1.0.0

YUI currently has 7 components with performance tests using [Benchmark.js](http://benchmarkjs.com/), but all being sourced from different places, and none from inside the `yui3` repo.  Seems like it would make sense to include this in the source tree to standardize how developers include it in their tests.

Questions:
  1. While Benchmark.js never seems to update beyond v1.0.0 (despite code changes), someday there might be v2.0.0.  Should the path be versioned? (e.g. `src/common/vendor/benchmarkjs/v1.0.0/benchmark.js`)
  2. Are there any additional licensing requirements here, such as including the license in [/yui3/LICENSE.md](https://github.com/yui/yui3/blob/master/LICENSE.md)?  FYI, we have OSWG approval to include this in the source tree.