link: prepare marks

Also renames an object attribute to closer match the hoon code.

pkg/arvo/lib/link.hoon

@@ -139,7 +139,7 @@
     %-  pairs
     :~  'title'^s+title.page
         'url'^s+url.page
-        'timestamp'^(time time.page)
+        'time'^(time time.page)
     ==
   ::
   ++  comment

pkg/arvo/mar/link/action.hoon

@@ -0,0 +1,16 @@
+::  link: subscription updates
+::
+::TODO  this should include json conversion once mark performance improves
+/+  *link
+|_  =action
+++  grow
+  |%
+  ++  noun  action
+  --
+::
+++  grab
+  |%
+  ++  noun  ^action
+  ++  json  action:de-json
+  --
+--

pkg/arvo/mar/link/initial.hoon

@@ -0,0 +1,14 @@
+::  link: initial subscription result
+::
+/-  *link
+|_  =initial
+++  grow
+  |%
+  ++  noun  initial
+  --
+::
+++  grab
+  |%
+  ++  noun  ^initial
+  --
+--

pkg/arvo/mar/link/update.hoon

@@ -1,6 +1,5 @@
 ::  link: subscription updates
 ::
-::TODO  this should include json conversion once mark performance improves
 /-  *link
 |_  =update
 ++  grow