Refactor args parsing and config management for connect and create_pool

Added:

* `connection_class` parameter to connect() and create_pool() to
  specify a custom Connection object.

* `server_settings` parameter to connect() and create_pool() to
  set custom server connection settings.

Fixed:

* Connection pool to always create Connections with correct
  configuration.  Before, the pool could lose parameters like
  `statement_cache_size`.

Backwards Compatibility:

* connect() and create_pool() no longer accept arbitrary
  keyword arguments for server settings. Use new `server_settings`
  argument for that.

Author: 1st1

asyncpg/__init__.py

@@ -5,11 +5,12 @@
 # the Apache 2.0 License: http://www.apache.org/licenses/LICENSE-2.0
 
 
-from .connection import connect  # NOQA
+from .connection import connect, Connection  # NOQA
 from .exceptions import *  # NOQA
 from .pool import create_pool  # NOQA
 from .protocol import Record  # NOQA
 from .types import *  # NOQA
 
 
-__all__ = ('connect', 'create_pool', 'Record') + exceptions.__all__  # NOQA
+__all__ = ('connect', 'create_pool', 'Record', 'Connection') + \
+          exceptions.__all__  # NOQA

asyncpg/_testbase.py

@@ -18,6 +18,7 @@
 
 
 from asyncpg import cluster as pg_cluster
+from asyncpg import connection as pg_connection
 from asyncpg import pool as pg_pool
 
 
@@ -162,12 +163,14 @@ def create_pool(dsn=None, *,
                 init=None,
                 loop=None,
                 pool_class=pg_pool.Pool,
+                connection_class=pg_connection.Connection,
                 **connect_kwargs):
     return pool_class(
         dsn,
         min_size=min_size, max_size=max_size,
         max_queries=max_queries, loop=loop, setup=setup, init=init,
         max_inactive_connection_lifetime=max_inactive_connection_lifetime,
+        connection_class=connection_class,
         **connect_kwargs)