performancetest: Add benchmarks for raw UTF-8.

Jackson has a special codepath for parsing JSON directly from UTF-8, which is the common case since that's how JSON is usually stored.  This avoids the overhead of going through an `InputStreamReader` layer.  This is part of what makes Jackson so fast.

I added a benchmark to measure the raw UTF-8 case for Jackson.  All the other parsers are benchmarked using `InputStreamReader` to do the conversion, since I don't think any of them have a raw UTF-8 mode.

(I also updated `CaliperRunner` to accept command line arguments.  Can split this off into a separate commit before doing the final push.)

Here are some preliminary results (from my laptop, so probably not very reliable):

![screenshot 2014-12-18 07 29 11](https://cloud.githubusercontent.com/assets/239989/5490647/d0309ebc-8687-11e4-9b50-4fc72586b2cf.png)