api: native crud module support

Adds native api support for crud module [1]
to use it from a connection object.

1. github.com/tarantool/crud

Closes #205

Author: GRISHNOV

tarantool/connection.py

@@ -86,6 +86,7 @@
     warn
 )
 from tarantool.schema import Schema
+from tarantool.crud import Crud
 from tarantool.utils import (
     greeting_decode,
     version_id,
@@ -516,6 +517,7 @@ def __init__(self, host, port,
             IPROTO_FEATURE_WATCHERS: False,
             IPROTO_FEATURE_GRACEFUL_SHUTDOWN: False,
         }
+        self.crud = Crud(self)
 
         if connect_now:
             self.connect()