Emit the difference between fast.js and build in method

Fixes #34.
How about this:

- we check if the second suite starts with `fast`
- if so, we assume there is a first entry which is our `Native` implementation
- if not, then use the slowest version to compare against

In the case of the later example, the output needs to be adjusted (saying something like "Result: fast.js is faster as xxx by 100%", where xxx might be `underscore.clone()` or `lodash.clone()`).

Does this make sense @phpnode?