Fix boolean conversion in arguments

It would summon `bool()` for conversion, which is always True except
when string is empty.
Now is using configparser.ConfigParser._convert_to_boolean. Much more robust

lib/__init__.py

@@ -35,15 +35,22 @@ if not path.isfile(_config_file):
 
 _config.read(_config_file)
 
-_supported_types = {t.__name__: t for t in [int, str, bool, float, type(None)]}
+
+def to_bool(x=None):
+    if x is None:
+        return False
+    return _config._convert_to_boolean(x)
+
+
+_supported_types = {t.__name__: t for t in [int, str, float, type(None)]}
+_supported_types['bool'] = to_bool
+
 DEFAULTS = {}
 DEFAULTS_TYPES = {}
 for k in _config.options('defaults'):
     tp_str, val = _config.get('defaults', k).split(',')
     tp = _supported_types[tp_str]
     val = val.strip()
-    if tp_str == 'bool':
-        val = _config._convert_to_boolean(val)
     DEFAULTS[k] = tp(val) if val else tp()
     DEFAULTS_TYPES[k] = tp