feat(policies): add CommentPolicy, update? and LikePolicy

examples/blog/app/policies/comment_policy.rb

@@ -0,0 +1,25 @@
+class CommentPolicy < Prism::Policy
+  def update?
+    user && record.user_id == user.id
+  end
+
+  def destroy?
+    update?
+  end
+
+  def restore?
+    update?
+  end
+
+  # Approving/rejecting is a moderation call, not an authorship one - it
+  # belongs to whoever owns the post the comment hangs off of, same as the
+  # nested-attributes moderation form on PostsController#update (which goes
+  # through PostPolicy#update? instead, since that request targets the post).
+  def approve?
+    user && record.post.user_id == user.id
+  end
+
+  def reject?
+    approve?
+  end
+end