Adding a Waiting Reservation class

I'm still not 100% comfortable with this approach but for now I think we
can get something working and then think about something else. Otherwise
nothing will be accomplished.

Related to #2

lib/deustorb/reservation.rb

@@ -1,4 +1,7 @@
+require 'deustorb/reservations/waiting'
+
 module Deustorb
-  class Reservation
+  module Reservation
+    WAITING = 'waiting'
   end
-end
+end

lib/deustorb/reservations/waiting.rb

@@ -0,0 +1,13 @@
+module Deustorb
+  module Reservation
+    class Waiting
+      attr_reader :id, :status, :position
+
+      def initialize(options)
+        @id = options.fetch(:id)
+        @position = options.fetch(:position)
+        @status = Reservation::WAITING
+      end
+    end
+  end
+end

spec/deustorb/reservations/waiting_spec.rb

@@ -0,0 +1,32 @@
+require 'spec_helper'
+module Deustorb
+  module Reservation
+    describe Waiting do
+      def reservation
+        Deustorb::Reservation::Waiting.new(id: 'some-id', position: 3)
+      end
+
+      it "has a waiting status" do
+        expect(reservation.status).to eql(Reservation::WAITING)
+      end
+
+      it "has an id" do
+        expect(reservation.id).to eql('some-id')
+      end
+
+      it "has a position" do
+        expect(reservation.position).to eql(3)
+      end
+
+      describe "#initialize options" do
+        it "requires an id key" do
+          expect{ Waiting.new(position: 3) }.to raise_error(KeyError)
+        end
+
+        it "requires a position key" do
+          expect{ Waiting.new(id: 'some-id') }.to raise_error(KeyError)
+        end
+      end
+    end
+  end
+end