Feature/soledad adbapi3

DO NOT MERGE YET
just for testing / pullreq purposes

How will this relate to adbapi's close methods? We have to ensure everything is closed before returning from this method, otherwise we may have orphan file descriptors hanging around after client shuts down. My current limited understanding is that Twisted reactor works with multiple threads, but we must be sure we know how things are cleaned up to ensure it happens correctly.