Support @user/node in [[wikilinks]].

app/agora.py

@@ -158,6 +158,7 @@ def node(node):
             )
 
 @bp.route('/node/<node>@<user>')
+@bp.route('/node/@<user>/<node>')
 @bp.route('/@<user>/<node>')
 def subnode(node, user):
 

app/util.py

@@ -57,7 +57,8 @@ def canonical_wikilink(wikilink):
         wikilink.lower()
         # chars that convert to -, slug-like.
         .replace(' ', '-')
-        .replace('/', '-')
+        # not a good idea in the end.
+        #.replace('/', '-')
         .replace('\'', '')
         # chars that are elided.
         .replace('%', '')