Add pagination to commands collection

The commands collection, which can grow quite lengthy, currently does not
allow any pagination. This provides the "start" and "limit" query arguments,
which are present for many other collections.

app.rb

@@ -558,8 +558,9 @@ def render_template(name)
   #
   # @todo danielp 2013-06-26: this should be some sort of discovery, not a
   # hand-coded list, but ... it will do, for now.
-  COLLECTIONS = [:brokers, :repos, :tags, :policies, [:nodes, {'start' => {"type" => "number"}, 'limit' => {"type" => "number"}}],
-                  :tasks, :commands,
+  COLLECTIONS = [:brokers, :repos, :tags, :policies,
+                 [:nodes, {'start' => {"type" => "number"}, 'limit' => {"type" => "number"}}],
+                  :tasks, [:commands, {'start' => {'type' => 'number'}, 'limit' => {'type' => 'number'}}],
                  [:events, {'start' => {"type" => "number"}, 'limit' => {"type" => "number"}}], :hooks]
 
   #
@@ -692,7 +693,18 @@ def render_template(name)
   end
 
   get '/api/collections/commands' do
-    collection_view Razor::Data::Command.order(:submitted_at).order(:id), 'commands'
+    limit = params[:limit]
+    start = params[:start]
+
+    raise TypeError, _('limit must be a number, but was %{limit}') %
+        {limit: limit} unless limit.to_i.to_s == limit or limit.nil?
+    raise TypeError, _('start must be a number, but was %{start}') %
+        {start: start} unless start.to_i.to_s == start or start.nil?
+    limit = Integer(limit) if limit
+    start = Integer(start) if start
+
+    collection_view Razor::Data::Command.order(:submitted_at).order(:id),
+      'commands', limit: limit, start: start, facts: true
   end
 
   get '/api/collections/commands/:id' do