Let jOOQ keep open PreparedStatements

We're going to be implementing a series of performance improvements for the issue you've helped discover in jOOQ: https://github.com/jOOQ/jOOQ/issues/3225

To be fair, the jOOQ benchmark could profit from keeping open `PreparedStatement` references between consecutive query executions. It won't make too much of a difference given the bottleneck in https://github.com/jOOQ/jOOQ/issues/3225, but at least it is more comparable to the plain JDBC solution.

We'll keep you posted, and thanks again for helping us discover this issue
Merge pull request #122 from lukaseder/patch-2

Let jOOQ keep open PreparedStatements