[Docs] Add/update docstrings and license text in every file

calsocial/calendar_system/__init__.py

@@ -1,15 +1,48 @@
+# Calendar.social
+# Copyright (C) 2018 Gergely Polonkai
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+"""Calendar system base definition for Calendar.social
+"""
+
 class CalendarSystem:
+    """Base class for calendar systems
+    """
+
     __has_months__ = False
     __has_weeks__ = False
 
     @property
     def day_names(self):
+        """An iterable of day names
+        """
+
         raise NotImplementedError()
 
     @property
     def month(self):
+        """The name of the current month, if applicable
+
+        It may include the year.
+        """
+
         raise NotImplementedError()
 
     @property
     def days(self):
+        """An iterable of days to be displayed on the month view, if applicable
+        """
+
         raise NotImplementedError()