Performance tests

This adds performance tests for a basic SELECT mapping query against many Java ORMs. Also, the readme is now markdown and includes the performance results. 

**Included:**
* Hand-coded JDBC ResultSet (the benchmark)
* sql2o
* [hibernate](http://hibernate.org/)
* [JDBI](http://jdbi.org/)
* [jOOQ](http://www.jooq.org)
* [Apache DbUtils](http://commons.apache.org/proper/commons-dbutils/)
* [MyBatis](http://mybatis.github.io/mybatis-3/)
* [Spring JdbcTemplate](http://docs.spring.io/spring/docs/4.0.0.RELEASE/spring-framework-reference/html/jdbc.html#jdbc-core)

The basic idea of each performance test is to set up a connection in the constructor, then time how long it takes to execute the `run` method 1000 times.

* See the [readme results](https://github.com/aaberg/sql2o/tree/performance_tests#performance)
* See the [actual tests](https://github.com/aaberg/sql2o/blob/performance_tests/src/test/java/org/sql2o/performance/PojoPerformanceTests.java#L128)

**TODO BEFORE MERGING**
* update the readme with results from a fast machine

We could add more down the road, like:
* [EBean](http://www.avaje.org/)
* [JdbcHelper](https://code.google.com/p/jdbc-helper/)
* [Yank](https://github.com/timmolter/Yank)
* [OrmLite](http://ormlite.com/)
* [JaQu](http://www.h2database.com/html/jaqu.html)
* [iciql](http://iciql.com/)

Other interesting ORMs that we won't test against (for now):
* [persism](http://sourceforge.net/p/persism/wiki/Manual/) - not available via maven