Feature/soledad adbapi3

DO NOT MERGE YET
just for testing / pullreq purposes

I'd add docstrings more or less like this:

    """
    Return a connection pool.

    :param opts: Options for the SQLCipher connection.
    :type opts: SQLCipherOptions
    :param openfun: Callback invoked after every connect() on the underlying DB-API object.
    :type openfun: callable
    :param driver: The connection driver.
    :type driver: str
    """