update doc

Author: neurobin

ocd/types.py

@@ -4,7 +4,7 @@
 __author__ = 'Md Jahidul Hamid <jahidulhamid@yahoo.com>'
 __copyright__ = 'Copyright © Md Jahidul Hamid <https://github.com/neurobin/>'
 __license__ = '[BSD](http://www.opensource.org/licenses/bsd-license.php)'
-__version__ = '0.0.1'
+__version__ = '0.0.2'
 
 
 class SingletonMeta(type):
@@ -66,3 +66,4 @@ def __setattr__(self, key, value):
 
 # this one needs to be defined here.
 Void = object.__new__(VoidType)
+'''Used internally to represent non-existent value, thus `None` retains its usual meaning.'''