add connections pool support
Interesting, I had not heard of dbutils.  Thanks for sharing this!

Regarding merging this, a third-party library dependency is not something I want to add to peewee.  It might work better as a module in `playhouse`, though -- this is where I've been buliding little extensions to peewee.  Another note, if you're wanting to merge in new functionality for peewee, I also like there to be tests and documentation.

Thanks again!

The connections pool is based on DBUtils and it works fine for me except that count() method of SelectQuery always return 0. But I can get the count with

``` python
Foo.select(fn.Count(Foo.id).alias('count')).get().count
```
