Adds Underscore.js and Lodash.js to the benchmarks

Unfortunately, it looks like lodash consistently outperforms fast in the `.forEach()` test, and occasionally in the Array tests with `1000` items.

This *could* just be a matter of using a while loop instead of a for loop, at least on the occasional wins for lodash.

Lodash's `forEach` also uses a `while` loop, but on top of that, they don't set the context each time using `call`. They'll call the function using traditional notation unless you specify a context. I'm not sure if `fn.call()` is slower than `fn()`, but it's a possible reason for lodash's success.
@jdalton i think this is a great example of why there's room in the world for both fast.js and Lo-Dash - they're different solutions for different problems. Lo-Dash for consistency and general sugar, fast.js is for raw speed in the cases where it's really required.