Add user tripcodes

Users can separate their name and a password with ## to create the
illusion of consistent posting.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/models.py

@@ -90,6 +90,8 @@ class Post(models.Model):
     )
     # User's supplied name for this post
     name = models.CharField(max_length=255, null=True, blank=True)
+    # User's tripcode, already calculated
+    tripcode = models.CharField(max_length=10, blank=True)
     # User's supplied subject for this post
     subject = models.CharField(max_length=255, null=True, blank=True)
     # Text of this post