Removed img_dir from set method, added specs

spec/api/api_settings_spec.rb

@@ -15,4 +15,24 @@ describe Squib::Deck do
 
   end
 
+  context '#set' do
+
+    it 'puts font in @font' do
+      deck = Squib::Deck.new do
+        set font: 'foo'
+      end
+      expect(deck.font).to eq ('foo')
+    end
+
+    it 'raises deprecation errors on img_dir' do
+      set_img_dir = Proc.new do
+        Squib::Deck.new do
+          set img_dir: 'foo'
+        end
+      end
+      expect { set_img_dir.call }.to raise_error('DEPRECATED: As of v0.7 img_dir is no longer supported in "set". Use config.yml instead.')
+    end
+
+  end
+
 end