add some doctest cases of anyconfig.tests.common.MaskedImportLoader
fix a potential bug that kwarg parameter sep not used in anyconfig.backend.ini_._to_s
add a hack to silence pyflakes warns that some modules are imported but not used in anyconfig.compat
make _dummy_fun returns a empty dict to make parser returning empty result even if yaml moduel is not found in yaml backend
make _dummy_fun returning None (when no xml modules available) and process such cases in etree_to_container (xml backend)
try to silence pylint warns a definition of a function 'cmp' overwrite built-in, in anyconfig.backend.backends
fix a potential bug that list_parsers_by_extension() try to access to a protected member '_extensions' in anyconfig.backend.backends