Categories: Make "calendar"

This will keep calendar/schedule pages more organized.
Signed-off-by: Ethan Madison <ethan@ethanmad.com>

content/add_calendar.md

 +++
-categories = ["general"]
+categories = ["calendar"]
 date = "2016-08-24T15:35:56-04:00"
 tags = ["document"]
 title = "Add Our Calendar"

content/schedule.md

 +++
-categories = ["general"]
+categories = ["calendar"]
 date = "2016-06-24T14:34:02-07:00"
 tags = ["document"]
 title = "Schedule"