Connection pooling

[dutchmartin]

We want to be able to use sprattus in a high performance web application. Therefore, connection pooling and maybe combining that with pipe-lining makes a lot of sense to do.

To come to an implementation, the following points are the concrete todo's:

• Look at the existing connection pooling solutions and find one that is async
• implement an async connection pool if it does not exits yet.
• Add support for sprattus and create benchmark results.