add method that tests if keen project id is set
method keenio.keen_io_writable() renamed to keenio.keen_is_writable()
method keenio.keen_io_readable() renamed to keenio.keen_is_readable()
use keen_has_project_id in keen_is{writ|read}able()
improve test for keen_is{writ|read}able() methods
remove unnecesary parentheses
fix indentation