Expose parsed db url
Nice! Do you mind adding a test-case for the new function?
 Sure, :+1: ?
 Thanks!

It'd be useful to get the parsed dict from db_url so it could be used with pooled connections as well.
E.g.:

```
db = PooledMySQLDatabase(
    max_connections=32,
    stale_timeout=300,  # 5 minutes.
    **db_url.parse(app.config['DATABASE_URL'])
    )
```
